Thank you all for the advice, think I'll start with replacing the pads with Koolstop thin line salmon or dual and see how it goes before adjusting the straddle cable... lots to learn!

Powder coating can be a bit of a minefield, there's a range of both coatings and techniques, I've seen some really exquisite paint like finishes and some that would be disappointing on a garden gate. Ideally you need to go by personal recommendations, preferably from those who had it done some years ago. It isn't even the case that paying more gets better, there's a local company that works primarily with train components who's work is the smoothest deepest gloss, but you have to accept the colour they're using and even then they're not always interested.  If you're lucky and meet those criteria, and do the frame prep yourself, it's very cheap.
I use Maldon Coatings, well twice, I chose them on the basis of seeing several frames I was impressed by, bikes and motorbikes.  They do things a bit differently, an alkaline paint removal to lessen the need for blasting which when needed is done with softer plastic beads, phosphate bath which also cleans out the inside of the frame, then a frame inspection, followed by epoxy primer, then as many top coats as you've paid for.  If you want decals they'll lacquer over them with a polyester two pack, or you could choose a clear final coat and decide on the level of gloss. Then all work carries a five year anti corrosion guarantee.  You pay for that of course, I think the last frameset cost £160, without going overboard with extras.  I'm not saying I couldn't have got a good job done cheaper, but I was happy to pay the extra for the certainty.  They don't want you to do any frame prep, apart from it being clean, they use specific rubber bungs for the treads, it doesn't leave the abrupt edge you get from using bolts.
https://www.msbpcl.co.uk/our-work/bicycles/

Thorn of course have moved away from powder coating, on to a DuPont two pack polyester wet finish.  I've been impressed, where it gets a knock, it tends to result in a scuff rather than a chip. And the depth of colour is excellent, the photos don't do it justice.  If I were refinishing another frame and I was wanting it to look its best, I'd have this done, or at least a polyester top coat.

If you do fit decals will you have to spray lacquer over the top?

Usually decals on powder coated frames are not lacquered over.  even on new bikes such as Surly or even up market ones like Shand.  Thorn were a bit of an exception, not sure how it was done, but the lacquer wouldn't have been as tough as the powder coat.  You can get clear PC, but it requires a temperature that's likely to burn any decal.

What B cereus said. For low and mid profile brakes the lower the yoke the longer the virtual lever and the less pad movement for the same cable pull, less pad movement equals more force - If you imagine a horizontal line from the boss and a line from the yoke continuing through the attachment point, where they intercept is the leverage.
With wide arm canti's it makes no difference, the arms are already horizontal.

Thanks folks. Really appreciate all the advice.

I was really just looking for the views on sandblasting and powder coating / painting.

My pal at the LBS knows to plug all holes and remove everything from the frame. Bits like brake cables / shoes will be replaced as required.
( Good advice on greasing the inside of the frame ).
I also have a new front ring and rear ( old style ) cog to fit. Plus chain.

It looks like I'll go with the powder coating. And stick to black.
But all further views appreciated.

I'm looking to get the Raven ship shape for a Summer Scottish tour ( depending on my recovery from the cancer op I had last Nov. - I start a second round of Chemo next week ) and then perhaps pass it on to a Thorn enthusiast who can take it abroad for a long tour it loves. A lot of good memories are built into that bike. Only fare to let go rather than keep it tied to an old fella who can't make full use of it.

Once again, all comments appreciated.

Matt