Here's my thoughts on a GT40. They are free so they inherently have no value. But for what it's worth, here it goes. My decision list goes like this. They all should be selected for the same goal.
First: Budget then:
1. Power train capability/limit. (1 and 6 should be the same within - = 0, + = 15-20% of power number.)
2. RPM range of engine. (See 4. practical rev limit of Hyd Lifter is 6000 rpms)
3. Octane of fuel. (Street gas will limit CR to about 10.5 to 1 with alum heads.)
4. Lifter type, (use hyd roller cam. need more power? make engine bigger not rev higher)
5. Available in hand usable parts. (see first)
6. Desired power. (a really strong street number is 375hp, 25 more, 400, will all be above 5500 rpms and rarely used.) >500...…………...great bench racing.
So a [email protected]
375HP is 1.24hp per CI that is a good number for 93 octane pump gas. The same heads/cam/CR that make that number on a 302 will make about 400 with a 331 and 425 with a 347. That (425) is very close to the long life street engine number for a stock Ford block.
So now what? If you have a good stock block and crank, reuse them and build a 305 (bored over .30 standard 4 inch bore, standard stroke crank. Use ARP main and rod bolts and have the block line bored. Balance the whole rotating assembly including flywheel, hormonic balancer, clutch pressure plate as close to perfect as possible. Convert to hyd roller cam if you have older block. Then the worries about cam/ZDDP/new oil wear are over.
Select pistons to achieve 10 to 1 CR.
Heads: I have seen several SBF use Edelbrock RPM Performer alum heads and make north of 400hp on 305 CI.
Cam: Comp and others make a good hyd roller in the 280 degree (both in/ex, will have good idle and run up to 6000 RPMS well) and .540 lift range. Keeping lift under .55 will extend spring life and generally will work well on a long life street motor.
IMHO: reusing a good stock block/crank/rods, limiting revs to 6000, real good heads, a hyd cam selected to rev range and street use and a really good balance job with ARP hard wear will make 375-400 HP on pump gas. It will last the lifetime of the car and pull like a friggin monster when you want it to.
As you can see 331 or 347 really isn't necessary.
As an aside the power train will work well if you have a upgraded input shaft R21 and live a long life.
Last but should be first! Use the money you have saved to put a Quaife TBD in the gearbox! The difference between a open diff and a TBD are so profound that I can't
over emphasize how big a deal this is.
Last, really last this time: Some one once said "Decide if you what to talk about it or drive it. Many a great hotrod has been ruined by putting too much power in it"