1997 4L60E to Vortec 5.3 or 6.0L

[autowrench]

I am planning to swap a 5.3 or 6.0 Vortec into my 59 Chevy Apache sometime in the near future. I do not have one picked out yet. I have an opportunity to remove a 1997 4L60E from a GMC 1500 Savana van. It is mated to a 305. Everything I have learned so far is that the bolt pattern does not match exactly and the the input shaft is different from versions that came mated to the Gen 3 engines. What I don't know is if this would be difficult or expensive to make work. The transmission was working when the snow caused the building it was in to collapse and wreck the van. Is it something I should get? I don't think a rebuilder would want to take it as a core for a rebuilt exchange transmission. Thanks for any input!
Tom