[DougD]

Blackout
A 390 can be a good choice. It is dimensionally the same as the hallowed 427, and can be dressed up to look like one. Only an expert will be able to tell the difference. With aluminum Edelbrock heads and intake, it can shed some of that big block weight, too. If you find one from a T-bird, be sure to grab the radiator "puke tank" from the front of the intake manifold. You'll need it in a Cobra.

I have a Ford Racing crate small block in one of my cars. No issues, and it runs strong. It was an economical alternative to having someone build one for me.

Power steering is subjective. Some build Cobras with PS, but most do not. With wide tires on the front, a Cobra can be kind of difficult to steer at low or no speed. But once rolling, it's really not needed. Your choice.