Surprisingly the best 904 I ever had was the one in my 87 Dodge B 250 van. That was the most trouble free 904 of the many I have owned.
My 78 fury has one in it too, so far so good (but hell, that car has only 56k miles) but is starting to show issues from age... Hardened seals within the clutches, etc. That one I am gonna overhaul and put back in but not without a few upgrades.
I could be wrong but I had a few B200 and B300 vans and they were all 727's with a 8 3/4 rear or dana 60. The rears will fit in a "B" body. Just a 1/2 inch wider, I believe. Many years ago. The dana's were 8 lugs, so could not be used easily.