Odd Triumph question for the pros

okay so i have the opportunity to pick up a triumph unit 500 engine and some other parts very cheap. I was searching around and found out that 500 unit guts and top end can go into a 350 unit cases.

Question is can the 500 unit guts and top end go into 350 pre-unit cases? or even 500 pre unit cases?

I think i'm going to grab this b/c the price is too good to not, but i've always wanted a preunit over a unit triumph.