Thanks, I've been doing a lot of reading about the Mk2s and have invested in Michael Harris' book on the subject. (Stupidly it cost less for me to get a copy of that book from Amazon Germany including postage than it did to get it from Amazon UK!) I think I've managed to get around most of the detail differences behind this supposedly "standard" design!
I've stockpiled a few cheap Bachmann Mk2 brake coaches and FKs which are going to lend their roofs and chassis (suitably altered) to the Lima coaches. I'm planning on trimming down the extra height at the bottom of the Lima body, removing the paint guide line on the body and then attaching the Bachmann chassis. The Bachmann roof goes straight on once they're trimmed by about 2mm at either end. I'll probably use as much of the Bachmann glazing as I can as well. Any left over I was planning on using SE Finecast glazing which seems acceptable to me based on photos I've seen.
As I mentioned this is all very experimental so the less money I can spend the better. If I can get a convincing result I may consider Shawplan parts in the future. No doubt they are going to be high quality, but you pay for that quality! It would be wasted on before I got some practice in first.