The V-6 was an interesting design. GMC also built a 702 cid V-12 version. V-12 block, cam, crankshaft. and distributor. Add two pair of V-6 heads, two pair of V-6 exhaust manifolds, and two V-6 intake manifolds.
There were Diesel versions of the V-6, along with a V-8 variant.
The 305 was the little guy. Other gasoline V-6s were 351, 401, and 478 cid. As you might expect, this thing was BIG and HEAVY.
"I" would be looking for a 401 or 478 to stuff in that pickup. Talk about novel!
http://www.6066gmcguy.com/index.php