Geoff it is one of the 4 400's
one of the two 1980 T's the one you were working on though was my 400x but I pulled the top end off that saturday to inspect and it is all good but the one it is pictured on is my first PE.
I have a PE250b project too and I don't have a pipe for that I split the crank cases yesterday and I will replace some stuff in there.
I took the 400 with your pipe around the front yard though riping the lawn up mum hasn't noticed yet, it was not much louder than the stock pipe and it sat there idling well and seemed to rev cleanly I think it will be a very good pipe I will give you more of a review when I take it for a big ride.
I also have a PE175n but I don't know if i will do that up yet maybe later.