702 GMC V-12 powered '62 GMC 1-ton

[A.T. RockDriller]

Ok....
I sure didn't think I would be chipping in on this ....but.......
Here ya' go.
Me, having a GMC V-6 in the ol' '63, right out there in the driveway, affords me the opportunity to speculate in person on the dimensional challenges at hand.
First of all....I sure wish you had a mid-'60's GMC to relocate that power-plant into.
That being said, The double six configuration...(other than the weight) sure wouldn't interrupt the passenger compartment nearly as much as you might think.
I encourage you to measure twice on this one.
If you were to mount it so the front six sat a few inches forward of where the stock V-6 sits....shorten up the fan assembly....cut the firewall and floor-boards a bit.....you might be able to get by with picking up the dog-house engine cover off of a P-30 van or something like that.
Bucket seats, a little fabbing....convert the "industrial/Truck bell housing bolt pattern to the light truck set-up...
Maybe go with an over-drive automatic tranny.
The weight thing sounds bad, but it's no big thing to put 1500 pounds over your steer axle. Some of that weight will transfer back anyway.

I'm thinkin' it might not be that extreme of a conversion, if you look closely at the amount of real estate available behind the core-support.
Maybe.

We'll be watchin' you.