Hi Nigel,
I'm a member of the LYRS myself, though last time I asked for drawings etc, the B. C. Lane Drawings came back, which are the ones in the Jenkinson book. I'll have to have a trip out to Manchester when things start opening up again. I do have it on good authority though that the LYRS is working on a book of carriages and their drawings.
I did do some bogie designs for 3d printing as an exercise in whether it could be done, but my pal who does the 3d printing hasn't got round to it yet - this was to see if functional parts were possible.
I work in a similar way, converting the dimensions on a spreadsheet. Although the last one I worked from I marked up the drawing in red with the 2mm scale dimensions - this was for 3d printing.
I think 3d printing has its merits for enclosed structures, but as you say for cab side and roof, etched parts will give the correct scale thickness needed. Likely in the future I will have a go at doing a proper etch for the class 28. My list of things to have a go at gets longer and longer.
I should stop being a hobby butterfly with many unfinished tasks and I should concentrate on getting my trackwork finished and wired up. Like I've seen in Geordie Exile's tagline It's not "a bunch of unfinished projects", it's "slow-burn multi-tasking".
Adam