429 CJ's came as an option those years and they didn't have to move towers like the 69, 70 Boss 9's. I sold a regular 429 (same block) to a kid who put it in his 73 a few years back to replace his 351. I think he just bought 429 cj frame pads from a wrecking yard and used the stock 429 motor mounts. Be sure to hog out yer exhaust ports before you put it together again, if you have'nt already. Otherwize all your speed parts are for not. Also use either aftrmarket rods or fords's CJ rods, with the football shaped rod bolt heads. They can be found on many 460 truck cores. That's where I got mine. CjJ oil pumps are an improvement over stock. Also Boss 9's use 1 more mill clearance stock over passenger car cranks. If your crank is in good shape you can use boss 9 bearings, which have the extra mill dialed into it. If your are really into spending money, have the journals cut to chev 454 specs and use after market, chev rods made to the 460 length. Then you can offset grind it for more stroke if you want even more cubes....

jerry