it would help if you would fill in your signature and tell us where you live,etc.
My friend Coach Mike bought a 428 from Keith Craft that was stroked to 461. Great motor and very streetable. Keith built the motor cheaper than we could have and it was dyno'ed and has a warranty. Oh, and it has 601 hp and 619 tq.
There are several FE motor builders on this site that can sell you a great FE for your Cobra. Call them.
I drive a small block but I love a big block Cobra
I have a couple of Cobra buddies that let me drive their FE Cobras.
If you want a big block, that's what you should buy. It's expense to change later. You never regret an FE in your Cobra.
Dwight