Greetings from down under. I can confirm that I have chassis P1726 & it is now the basis of the PA that I am rebuilding. I purchased the absolutely bare chassis a couple of years ago from Ray Fowler in Sydney. Ray wanted to purchase a J2 chassis quite a while ago & the deal included the P Type chassis as well. He had no use for it, so it had hung in the roof of his shed for years. I am rebuilding P1499 which had a very sad chassis (lots of corrosion & one broken rail). The fate of the original engine for P1499 is unknown (I'd love to hear from you if you know of 1705AP), so when a friend suggested a different chassis to keep my restoration moving, it seemed a good idea (no matching numbers to disturb). The attached picture shows where I am up to with the restoration. I hope to have it finished ready to be a part of a Pre-War MG rally here in Australia in October.
Elliot your restoration gives my hope to find MG 3880 (ex P1815 chassis change) a lift, or perhaps her parts as listed in previous have sustained others.