1970 Stingray Restoration Project- NEED HELP!!

Hello!  My father and I are trying to restore a 1970 Stingray.  We are beginning our restoration with the engine and transmission.  I know that my father wants to switch to an EFI engine, but wants to save the original (to rebuild at a later date).  I am trying to research as much as I can to find which engine would be the best swap.  Due to our time constrains we would like to buy a crate engine and a manual transmission (that will be able to support the new engine).  I would love to put an LS1 engine in it, but I am not sure if we have enough time or money.  If anyone has any advice on where we could begin looking for a new engine and transmission??  What to stay away from?  Key pointers we need to remember??  Anything that would really help us out??  I would really appreciate any advice!!  I want the vette to be perfect when we are done!  I want him to REALLY enjoy every minute of it and have no regrets about the engine and transmissions.  Any advice would be GREATLY appreciated!!!  

Thank you,
Elizabeth