You probably need to find a set of mounts for a 460 that fit up to your truck. Externally the 429 and 460 are the same. ONLY difference between them is the stroke and pin height on the piston. The only difference I'm aware of between a standard 429, 429 Cobra Jet, and a 429 Super Cobra Jet is the cylinder heads. Therefore, if you get motor mounts for a 460 (which I'm sure have to be kinda common for your truck) you should be all set. Good luck.
"Stuck with a m*par, Settle for a ch*vy, Happy with a Ford!!!!"
Tbird is right. I just put a 429CJ in a 77 F100 using 460 mounts found at PAW in Ca. They kept the engine level and still could use the oil pan and pickup that was on the engine, changing oil is tight when it comes to the drain plug , but manageable. if you need the number to PAW Email me Rodnwc@prodigy.net