The 427 was quite expensive even in the 60's. That's why Mr Shelby put 428's in some of the cobras! Not only that, you then need to chase everything else in the drive chain plus the brakes and it ends up even more money. They are brutish motors. So much power. A lot bigger and heavier too. I have one in a cobra. I have done plenty of clutches, props and tyres. One of them has to take the pain and eventually gives up!! (If you drive it like a cobra should be driven that is!)
Having said that, they are massive fun. I prefer them standard stroke, they make an amazing sound.