[xb-60]

Coldcomfort,
Follow your instinct and stick with something with a Ford badge in a Cobra replica.
I am using a SBF 302 Tickford engine (mated to a Toploader) in my AP FIA replica as it is from the same engine family as the original 260/289 Cobras. Attitudes here in Australia to engine choice are a little more....er.....lax....but over the pond, 90% of builders go with engines from the correct family in their Cobra replicas.
Cobra replicas are typically so light in weight that (IMO) you don't need to go chasing ultimate power to have the fastest car on the block.

Bottom line, though, is that it's your car, so go with what pushes your buttons. Enjoy the process!

Cheers,
Glen