Motorhome 727 trans in an A-body?

Without photos it's "just a guess." That is YOUR job, by the way. Photos that is. It will cost you about as much to have a slip joint shaft made as you can buy the parts and rebuild the 904. There are many threads on here, in fact there is a sticky

http://www.forabodiesonly.com/mopar/showthread.php?t=167607