Wow, neat project. You'll have 3 years to build it until he's 16. I did much the same thing with my youngest son. Bought a '72 Chevy Luv roller when he was 14. When he was 16, it had a 10 1/4" Olds 3.90 rear, TH400 and stock 455 Olds in it. We also put a full cage and window net in it with 5-point, 3" belts.

I'd start looking at the Chevy S10 frame and do some measuring. Even if you have to shorten or lengthen the frame, you'll have all later model running gear and steering in the old International and a 350 is pretty near a bolt-in, so of course a 4.3 V6 with a 5-spd would work really well.

Is he frothing at the mouth yet?