[750hp]

Les, the 3.75" (or even 3.7") cranks offer a greater range of rods and pistons. The 3.85 crank was designed as the budget stroker combo, using the standard 5.955 rods - 2.311 journal widths, and "less than perfect design" 302 pistons.

If you go with the 3.75 crank, you can run a 6" or longer rod, 2.1" journals, nice lightweight stroker pistons etc.

You won't hurt the motor - regardless of crank / rods / pistons / block. Any aftermarket parts will live a long and happy life in your Cobra.