Am I Crazy to Try This?

I would say go for it. there are a few guys on here that are more than qualified to talk you through it if something does come up. I too have rebuilt a few motors and ended up going through an allison auto in a dump truck and it wasn't that bad. just a bunch of tolerences really. I ended up buying my 904 already done but that was because I got a screaming deal and didn't have a core to work with anyway.