I just started doing this swap on a 47 (second series)(AD) truck I've talked to a few guys that have done it and it sounds like a good swap, I was given an S10 by a buddie too. In my case the S10 is a regular cab short box so it's only 108" so I'm gonna shorten my 47 bed in the front instead of lengthening the frame (Also not an option on your panel).
If the 4X4 was a 2.8 the V8 Swap should be pretty straight forward, check out Ebay Search for S10 V8 and you should be able to find several guys selling brackets that adapt the 2.8 stock mounts to a smallblock.
Good luck, and if you wanna check out my progress (not very far yet) you can hit my site
http://www.mongosgarage.com/S47/progress.htm Mongo
