429 into 70
I had a 429CJ that I found for cheap that I was going to put into my 'Alpha' '73, but after thinking about it for a while, and since I had not even dropped in the freshly-rebuilt 351CJ, I thought better of it.
Since you already have the trans for the 429 that saves you a few bucks there, now, along with the aforementioned motor mounts (trans mount and crossmember?), you're looking at major exhaust rework (either headers or trying to match up some kind of exhaust manifolds, then cooling, and as long as you have the 429 out you'll have to freshen it up, eh? Then there's the accessory brackets, belts and hoses, spark plug wires, fuel pump, water pump, probably an aftermarket intake manifold and related carb, Oh, you'll probably want a new torque convertor, shift kit for the new C-6, and I suppose you'll want to go through the trans as well.... It goes on and on, doesn't it.
Oh, and as long as you're putting in that big, heavy block, why not just make it a 460? Just change the crank and pistons. I will warn you though. A stock 460 does not like to rev much over 5200 or bad things start happening. Even with new forged TRW pistons, they come apart. There is just too much rotating weight. My buddies who race 460+ motors use lightweight pistons and steel connecting rods. Since making those two changes, their engines will last more than a half a season before blowing up like the stockers did.
BTW, my healthy 351C takes my '73 for high 12 second passes in the quarter. Fast enough?
You'll have to decide whether it is worth it for you or not.