Sorry to hear that about your engine. Is anything reusable? Block? Heads? Intake?
I'd be happy to discuss a new engine with you and maybe we could save some money on reusing some existing parts.
Most of my 427 Windsors are in the 550-600 hp range. The 550hp engines are very streetable, with hydraulic roller cams, pump gas, etc. It would most definitely take your Cobra to the edge without going overboard.
A lot of my customers are shy to ask for something with higher horsepower numbers, but the ones that are conservative always come back for a little padding down the road.
The good news is that Cobras have gas pedals and as long as they're streetable, you only have to give them as much gas as you feel comfortable with.