Originally Posted by KULTULZ
The 429 was not used in a MUSTANG until the 1971 model year other than the 69/70 BOSS and those were specially modified to take them.
While a 460 will go, it will require apron work. The car will then be nose heavy and only fit for straight road driving (hot street).
A lightly modified 302/351W will give you much more roadability unless you are just looking for flat out performance.
boss 429 1969/1970, rare, but they exist