A '68 427 will be a heckuva motor, but it's not quite the same as the NASCAR racing motor that grew the legend. Starting in 1968, the 427 was switched from solid lifters to hydraulic, and the rated HP dropped from 425 to 390. You would still get the cross-bolted mains in the block, the stress relieved casting, etc., a very fine motor, but not the great racing motor. You should pay less for a '68 427 than for the earlier solid lifter versions. (Although, the '68 engine can be converted to solid lifters.)
The 428 was Ford's effort to get big cubic inches in a street motor. It was a lot cheaper to make than a 427, and was never intended for pure racing purposes. Basically, a 428 is just a stroked 390, and tuned for massive torque over horsepower. The Cobra Jet 428 motors in Mustangs used heads from the 427, plus other enhancements to really put some hair on their chest. But, from the factory it was never as powerful as the (solid lifter) 427.
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427 - Essentially the rarest of the FE family of motor - built principally for factory "race cars" (and certian marine applications I believe) larger bore - shorter stroke - premium factory parts. Cross bolted bottom ends, modified oiling on some production runs (you have probably heard about "side-oilers") etc. NOS parts are very rare today and prices reflect it - IMO true 427's are not worth building unless you are restoring a car that was built with one.
428 - Also FE family. More common than the 427 but much less common than the 390/360/352 variants. Makes cubic inches with more stroke and less bore. Still generally a "performance" motor but not built with the same level of parts/care as the 427. Generally cheaper than 427 stuff but still not (IMO) cost effective to build (per HP given what you can get out of a 390 with aftermarket parts) unless you are restoring a 428 car or building a clone and want reasonable accuracy. That said - you can pretty easily replicate a 428 using quality late service blocks and aftermarket rotating assemblies.
429 - NOT an FE - this is a 385 series motor (same family as te 460). For pure HP/dollar you can probably get the most out of this engine at most price points if all you consider is the longblock build - the 385 series stuff is quite a bit more common than the FEs (although the FE crowd seems to be growing today and the aftermarket is attempting to get in gear). That said - you lose the cool factor of having an FE and if you have to modify mounts etc it might not be worth doing.
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In 1968, only the Cougar came with the 427
in 1969, only the T Bird had the 429
and if this info is wrong, tell me about it, but, you don't have to, I'm not going to memorize it and treat it as gospel. I'm sure other sources will say something else, but, again, I'm not trying to write the authoritative encyclopedia of everything automotive. Just sharing interesting stuff. In my spare time
