This topic has come up several times and I did review several of them.  I thought I'd share my efforts which are to upgrade the LMS and GWR vans in 00.  This is for a friend.   My starting point was a pair that had been severely knocked about.  I started off trying to salvage the underframes but it quickly became apparent that they were useless.   My reference is Historic Carriage Drawings, Vol 3, NPCs by Peter Tatlow, LMS Coaches by Essery & Jenkinson and LMS Journal 31.