I am posting the following for posterity.
Mating an Ortlieb quick release saddle bag to a traditional Brooks saddle can be accomplished with a little ingenuity.
For an example of what's possible, perform a web image search for the following KlickFix adapter:
KlickFix 316RIX3BR
Locate an image that shows the adapter installed on the rails of a traditional Brooks leather saddle. As you can see from that and the other returned images, if this adapter were installed 180 degrees in reverse of how it was intended, the flat portion of the bracket that the quick release is mounted to would be roughly parallel to the ground, A.K.A. positioned quite well relative to the requirements of Ortlieb's saddle-rail-mounted quick release bracket.
So, to modify the KlickFix adapter to work with an Ortlieb quick release saddle bag, locate a source for the KlickFix 216RIX3BR part and purchase one. Also, purchase or otherwise locate your preferred Ortlieb quick release saddle bag. Amassed together, these various parts will serve as the basis for the following hack.
Since the female KlickFix quick release mounted to the metal bracket is meant for a Gilles Berthoud bag, you can forget about the proprietary Ortlieb quick release being compatible with it. So, first thing you'll need to do is remove the KlickFix quick release from the aluminum bracket by unscrewing the two bolts, nuts and washers that fasten the two parts together. Once you've done that, I think you'll find that that the bolt hole pattern for the KlickFix quick release is different than the bolt hole pattern associated with the Ortlieb quick release (or maybe you're lucky and they match). To confirm, compare the pattern of the existing holes with the mounting hardware that came with your Ortlieb quick release saddle bag. So, assuming you can't simply plug and play, you now have two options. One, if able, and in an appropriate spot on the aluminum bracket, mark and drill two new holes that match the bolt hole pattern of the Ortlieb quick release mountain hardware. You may want dry fit everything before you drill anything. To do so, hold the bracket temporarily in place on the saddle rails while you check the positioning of the bag with the mountain-hardware-side of the quick release clicked into the bag. If you can position everything such that the secondary retention strap (i.e 'the Velcro strap") and associated bumper on the pointy end of the bag mate nicely with the seat post, than move forward as follows (and, if not, think over your remaining options).
Drill the holes and then, using some spare washers (maybe those culled earlier from the KlickFix adaptor) and the locknuts you've extracted from the other half of the Ortlieb mounting hardware, fasten the Ortlieb quick release to the aluminum bracket using the supplied bolts. Depending on the length of the supplied bolts it may be possible to keep the locknuts in the other half of the Ortlieb mounting hardware and to simply stack this part on top of the aluminum bracket (making a sandwich) and then bolt everything together that way. Also, you may find that you want to shorten the supplied bolts. If you don't know how to do this, perform a web search for a video since there's a trick to it.
To help picture all of this in advance, perform a web image search for the following Ortlieb part:
Ortlieb Saddle bag Mounting Set E97
...and compare the various views of the KlickFix adapter with the various views of the Ortlieb quick release mounting hardware. One note: the business side of the Ortlieb quick release mounting hardware (the side with the quick release mechanism) may require some support under those portions where the bolts pass through (i.e. the concave areas that are designed to lay against tubular saddle rails). If so, it might be preferable, using a belt sander laying on its back (or an machine tool belt sander) and a fine touch, to sand away (i.e. "remove") much of the problem area. If you do this just make sure that the end result is as flat/square as possible and that you don't remove so much material as to interfere negatively with the part of the molding that's directly responsible for the quick release mechanism.
Or two, if there is not sufficient material remaining or some other unforeseen complication arises than probably the easiest thing to do is fabricate a new bracket. This you can do if you're handy and have access to aluminum sheet material with a thickness that matches the thickness of the original bracket (or feel free to use stainless steel sheet of sufficient thickness for strength - use stainless washers to makeup the difference in thickness between the original aluminum bracket and the newly fabricated one if the latter is thinner - stack washers together when installing the hardware for fastening the bracket to the saddle rails). Otherwise, take the bracket around to your local machine shops until you find one willing to make a copy. Note: a raw copy will suffice. By this I mean that the machine shop need not relieve any material in relation to the needs of the old quick release mounting hardware since the quick release hardware you'll be installing (Ortlieb's) has no use for the various cutouts featured on the original bracket. If need be, to reduce fabrication costs, let them know that you'll finish the part (meaning that you'll sand/file the rough edges and polish and/or paint the raw aluminum). And, if you are handy with a drill/dremel/saw, you can even omit the various mounting holes/slots and relieved edges from your request and machine them yourself later (yours won't be as pretty as the machine shop would have done but who really cares?). Once you have the duplicate in hand, prepare it (drill the necessary holes and/or slots and, if necessary, relieve the corners to match the style of the original) and then install the Ortlieb bracket onto it as described above. With that complete and using the original mounting hardware (the stay fixing bolts, washers, locknuts and solid aluminum bar stock) install the modified bracket onto the rails of your Brooks saddle.
Although I find it odd that no one produces something like the adapter I've just described, this doesn't meant that those of who rely on Brooks saddles have to accept defeat. A little DIY design and fabrication can easily bridge the gap!
Good luck!
