Donor 318 car for $500 or 383 4-Speed for $1000.00??

You probably better start with the v8 car. While the motors out, put a little bigger cam and a little higher stall converter in it.
If you wanna big block later, you can do the DC K member conversion. http://www.bigblockdart.com/techpages/dck.shtml
If you don't know how to ID the 4 speed go here. http://www.bigblockdart.com/techpages/4sptech.shtml