Swap 904 to 727?

I know why some people want to be critical of others who are trying to be conservative on a restore. I think it would be foolish for someone not to look at all the options.
I am talking to someone in East Texas about a 8 3/4 rear end. Even though it will be quite a while before I will need it. If I can negotiate it early for $300, I think it would be better than waiting and giving $450, just because that is the asking price. That does not mean l am a cheapskate.