Hi - excellent work on the car so far, well done.
You may or may not know that Volvo designed the sills to be vented, to avoid trapping moisture in sills. Unfortunately what happens is leaves and other debris get into the vents under the windscreen, down the A-pillars and into the sills where the block the drain holes and the sills end up rusting from the inside out. Since your car has rust both in the A-pillars and the sills it's likely that the drain holes are blocked.
I've attached a photo showing how it's supposed to work.
I ordered a lot of panels from Brookhouse to repair a 1978 245 I used to have, I found the panels to be about 8/10. The steel is thick enough and coated both sides so that's good, but the pressings weren't 100% accurate (which is to be expected I suppose). I remember the outer sills didn't have the bends in quite the right place and the bottom bend needed to be made into a sharper 90 degree bend than it was. That said, I'd probably use them again.
I start the welding on this page of my project thread, which might be of interest -
https://www.volvoforums.org.uk/showt...=268976&page=5
I can't help with a suggestion of a supplier in Scotland unfortunately, the parts were posted to me from Brookhouse who are based in Norfolk.
Running wise, apart from the obvious full service I recommend taking the big rubber bellows off the K-Jet unit and cleaning the lifting plate etc. inside with brake cleaner, and then replacing the injector seals. Both easy to do.
Volvo themselves can supply the vast majority of service parts for these cars still, make sure you get original Volvo seals etc, the pattern ones have a habit of leaking prematurely.
If your brakes are seized, it'll be easiest to buy 4 new calipers and all new hoses - I have bought two complete sets of calipers from here and am happy with them, otherwise most motor factors can get them too.
https://brakeparts.co.uk/
Cheers