That's a good question.. he told me it was a Ford tranny behind the engine, and the stock rear.
As far as engine cost, I really don't know.. I saw a few rebuilt engines on eBay that were in the $2,000 range plus a core charge of $1500.. there's one on eBay now that's got a buy it now of $3500 plus a $1000 core.
I think when they say engine, they mean block and heads and thats it.. manifolds, starter, all that jazz is extra.
So in short.. my guess is a complete running engine like that is some bucks.. the guy who owns that GMC said he had quite a bit tied up in the new air starter and stuff.. and figured the engine stuff alone was worth in the $6,000 range.