351 = small block
429 = big block
You'll have to change a whole bunch of stuff putting a heavier, stronger engine in the car.
Suspension, transmission, rearend, exhaust....etc.
ADDED:
The 385-series 429/460ci Ford big-block started out as a sleepy, stodgy luxury car fat-block when it was introduced in 1968. It was a whisper-quiet big-block with abundant low-end torque for large sedans, and it did its job well. Ultimately, the 429/460 engine went on to power trucks, vans, and other types of Ford vehicles before production ended in the late 90s. The 429/460ci big-block had nothing in common with the FE and MEL series big-blocks of the era. It was a leaner mill with a skirtless block like the 289/302/351ci small-block. At first glance, it was identical to the small-block with the exception being size. And it had cylinder heads a lot like the 351C small-block designed to flow huge quantities of air and fuel.
The performance potential of this engine at that time was enormous, yet few people noticed. In the years since, both Ford Motor Company and the enthusiast have discovered the potential of the 385-series big-......
http://www.mustangandfords.com/techarticles/big_block_engine_guide/index.html