Hello Joe,
I have the 460/535 HP crate motor in SPF #343 backed by a Tremec TKO, runs great in all situations great on the road in fifth and all the power you could ask for in a street car. On the track it is a terrific combination that allows you all the fun and performance you want for once in while track events ( I only had it at one SAAC open track weekend). I have also driven a Ford 351 stroker crate motor and a custom built 351 SPF and those cars are a delight to drive. The difference is the low end torque....the owner of the SPF 392 stroker car and I swapped cars (Kept our respective wives with us) and his driving impression of the 460 was that there was significantly more power off the line and throughout the normal driving band ie: local access roads and pulling on to the freeway and driving down the road in fifth.
I also have a stroked 427 in my Unique that has as much if not more power than the 460 in my SPF. There is not enough room in the Unique for the 460....don't even think about it. The 427 is way more expensive than the 460 2x or more, you would be better served to look at the 351 crate motors if cost is a factor.
http://www.fordracing.com/parts/sear...ults/index.asp
The M6007D392 is under rated by Ford at 430 HP. The Ford car magazines have dynoed that engine at 470 -510 HP consistently with a good torque curve. Go to the web link above and look at the information available from Mustang & Fast Fords and the Ford 5 litre performance magazines. A little research will yield a huge amount of information for you to make a value decision.
For serious racing a truly custom built aluminum 460 or a fire breathing 351 are better choices. This is not an attempt to reinvigorate the BB/SB argument....To each their own.
Tony R.