If you can't use the horizontal dropout to achieve chain tension, there is a simple bodge that I use on my one remaining full size bike without a Chainglider:

https://surlybikes.com/parts/singleator

The bike on which I use this is an old VTT from the early 1990's designed for derailleurs, it has vertical dropouts and no means of fitting an eccentric bottom bracket without major surgery. I use this as a visitor bike at our island flat. It has a Nexus premium 8 hub, but the system would work just as well with a Rohloff.

I fitted the Singleator pushing up on the chain, with just enough tension to stop the chain falling off. So the extra friction caused by the one Singleator pulley is not really noticeable, in theory it should be half the friction from a normal dérailleur, maybe less as the chain doesn't bend very much.

The downsides for me are :

- one pulley to clean (trivial).
- not possible to fit a Chainglider (a nuisance because this means more chain maintenance).

There are other brands of one-pulley tensioner that would probably work just as well.

Even an old derailleur would work (done this in the past), but it was more of a hassle to set up and clean.

Chainline on a Rohloff, I assume this is on a frame with conventional 135mm dropout spacing, not an extra wide hub for a fat bike.

I am not sure the numbers, so I will only talk concepts.

The Rohloff has two different splined sprocket carriers available, one is slim and one is normal.  Thus, there are two options you have for chainline, depending on which you use.

You said 24mm bottom bracket spindle.  I am guessing that is 124mm square taper bottom bracket.

Cranksets are generally much more expensive than bottom bracket spindles, so it might be more affordable to pick a crankset you like and then buy the bottom bracket that has the spindle length you need.  Finding a crankset that works with your bottom bracket might cost more in the end.

It is easy to buy cranksets for double chainrings.  If you get one of those, you can use the chainring in the outer position, or you can use the chainring on the inner position and use a bashguard in the outer position.  I have my chainring on the inner position, bashguard on outer position, photo attached.

Make sure your bottom bracket works with the frame you have, for example my Rohloff is on a frame that has a 73mm bottom bracket shell, not the more common 68mm.  Thus, I had to shop for a 73mm bottom bracket with the spindle length I needed. 

Rohloff hubs work with 8 speed chains, but if you have a 9 or 10 speed crankset, that will work with an 8 speed chain.  I have built up several bikes, both derailleur and Rohloff.  And a couple have 10 speed cranksets and 8 speed chains.  On a Rohloff, no problem with that at all.  (That is a minor incompatibility if a front derailleur is used with an 8 speed chain and 10 speed crank, but that is not your situation.)

I am running a chainline that is about 5mm off of ideal on my Rohloff bike.  This is by choice.  I wanted my Rohloff bike to have the same Q factor (pedal width spacing) that my derailleur bikes have, thus I wanted a bottom bracket spindle that was 10mm narrower than I was supposed to have for the ideal Rohloff hub chainline.  I could have used a spacer to push the bottom bracket off center, but chose not to, that would have reduced my chainline error.

That 5mm chainline error is not a problem at all.  I do have greater wear on one side of my sprocket teeth than the other side, likely the same with chainring, but it is not a bid deal.  When you consider that it does not really matter what gear a derailleur bike is in, they will always have some chainline error, I decided not to worry about a 5mm error when I built up my Rohloff bike a decade ago.

I know I did not specifically give you an answer on what to buy, but instead laid out the concepts.  Good luck with your build.

The OEM axel plate fits fine in the horizontal drop out on my bike. It’s not a Rohloff specific dropout. But it fits. The bike is a steel frame Surly Cross Check. 
Is there any reason this won’t work and provide the required torque anchoring? 
Keen to do this as it means I could loose the long torque arm. 
(Also I know it will mean I need some other way of achieving chain tension).

My wife's  Ike does not have the threaded sprocket.
So after we had a discussion about the gearing my wife said she is fine with the current setup.  She said after riding from Ohio to the Rockies she would be stro g enough!
One less thing to carry!

Hi Tom,

A slight variation on the valuable detail above.  I hope this is useful:

In my tour North-to-South through the Rockies & to the Washington coast in 2016, I used a 17 x 36 combination on my Raven, with 26" wheels and 1.6" Marathon Supremes.  That gave me a gear-inch ration of 15.6 in my lowest gear.

There were a lot of hills on that tour, but they tended to be long (say, 25 kms) with a moderate grade (4-6%). If memory serves, I used my 1st gear only 4 times in about 2200 kms -- twice on the Icefields Parkway, once south of Canmore in Alberta, and once in the States, west of Montana (would have to check the detail.)

Each time I used low gear, it was for about a kilometre to reach to summit of a particular pass, and the climb was no problem.

As a comparison:  On a 5-day ride in the hill country NW of Ottawa in 2021, I used my low gear about 15 times in 175 kms -- the hills were steeper (usually around 8-10%) and shorter, and on the whole, more demanding than what I encountered in the West.

Good luck to you & Kathy, and enjoy!

John