Thanks Doug.
A FE427 is the 'hemi' Big Block?
Would that even fit in the GT40 if modified, or scrap that thought?
If that is the case, I am just left with W/C if I have understood the FE thing meaning big-block, no?
So what in the Small Block world of Ford is the equivalent FE ownership concept, or there isnt one?
Ford made only a few of the SOHC 427's....most were sold to racers, but they can still be sourced on the used market these days (and some NOS might well still be available, but at a stratospheric price).
I'd suspect that since the MKII was built to handle the FE engine series, there might well be a chance that a SOHC model would fit, but the chains used to rotate the OHC's are quite long and the heads quite large...not to mention the header system that would be necessary. I have to believe that if it were likely, somebody would have already done so.
The W/C issue is complicated by the fact that there are two different sized Windsor engines, the "5.0" (302 Cubic Inch Displacement) and the 351CID version. The deck height (the distance from the crankshaft centerline to the machined surface onto which the cylinder heads are mounted) of the 302CID is 8.2", the deck height of the 351CID is, IIRC, 9.2" (although there were some made with a 9.5" deck height--check out Dean Lampe's RCR40 build thread for a good look at one).
Here's a Wikipedia article on the Windsor engine line, a lot to be learned here:
Ford Windsor engine - Wikipedia, the free encyclopedia
As for a small block equivalent of the Hemi, well, no hemispherical combustion chambers there, but a few come to mind:
First and foremost would be the 271HP version of the 289 engine, called the "K-Code" or "Hi-po" 289. It was a fantastic engine, would rev freely and quite high, and had great street manners. Caroll Shelby made a great deal of money by upping the output to 300+ horsepower and putting them in a Mustang...remember the Shelby 350 Mustangs?
Next would probably be the Boss 302 engine....original versions of the Boss 302 Mustang sell for huge figures in the auctions.
Ford did make a "Boss 351" that was quite the runner at high RPM's. It had even larger valves/ports than the regular 351 4-V and was factory fitted with 4-bolt mains, solid lifter camshaft and adjustable valvetrain. It was available for only about 3 years before Ford discontinued it due to increasingly stringent pollution guidelines. It was a good motor, but the huge "sewer-sized" ports left something to be desired when low-RPM torque was needed....hang on at the higher RPM's, though!!
Nothing there with the visual impact of your Mopar Hemi or Ford's SOHC, though.
If it were me advising you, I'd say go with the 8.2" deck Windsor for two reasons...tuners can use aftermarket blocks and build them to incredible HP numbers (easily in line with the numbers you mentioned), and it is historically correct.
...however, having said that, I'm here to say that if I could afford a 40, it would have a 302-based Clevor in it....I'm a real fan of the broad torque curve those canted valve heads offer!
Cheers!
Doug