Peugeot (XD3TE) 2.5 Turbo Intercooled Diesel, as fitted to the 504 GTD Saloon – although I believe there are quite a few differences, sump etc between the two so probably best to rebuild yours?
If stuck I think Tom Ashworth still has an engine for sale and a rebuilt head – his contact details are on the front page of the website in the treasure trove bit…
Have you joined the club? Graham is a wealth of knowledge.
Good luck, it’ll be worth it!