Just got a reply from the engineer,
my question;
What are the options with regards to engines, is it only a case of meeting the IMS240 test and noise level requirements?
Answer;
Yep that's pretty much it. However on top of the IM240 and noise requirements the engine must also have a crankcase vent system and evaporative emissions control system equivalent to a current model engine in place, so if you run one of the older Ford motors you'd have to retro-fit the charcoal canister, vent/purge solenoid etc and crank case vent setup and all those parts from a more recent engine, so on a visual inspection the system will work roughly as well as a standard current model car.
Not sure whats involved with that, but doesnt seem like to high a mountain to climb, maybe!
The allure of a 427/428 is very tempting as opposed to the new kid on the block, Coyote.
But then again i couldnt deal with
oil leaks etc, my old 351 used to have a weeping rear main seal that was never quite right, sump gasket that would come and go. Are these issues gone with modern manufacturing processes or is it a case of, somethings never change.