429's are not FE engines. totally different. There never was a 429 FE. 427, 428 yes but no 429. 429/460 or what is considered the 385 series of engines. has No relationship to the FE series at all.
either way big blocks are not common swaps those that do tend to be one off deals and usually are into some type of racing where they really dont care about how it actually fits.