There's a guy on "Youtube" that stuffed a 455 Cadillac Eldorado front wheel drive unit,under an A.D. hood/cab.http://www.youtube.com/watch?v=28MRGe8dkx0 A Small block would surely be easier,but probably 47-ill a bunch of work. The V-8 should be shorter than the I-6,but you may have to change your steering box to the outside frame rail,to make room for the wider block. you may have to fab access to your firewall/trans. tunnel,but you could make an access door for your distributor,like the '60-'66 L.C.F.'s.Another guy set his cab on a '72 Chevy C-10 frame,and it looks like a sweet swap,but have no idea of the work involved. Sir Billy Marlow, (G.M.C. 860 Fabricator Extraordinaire), has another suggestion of mounting the engine behind the cab. This is "do-able",but limits your cargo space,unless you're planning on an elevated car-hauler platform. Good luck on your build!! Just a few suggestions. WELCOME to THE "Bolt"!!