I was just woundering, because the 93-95 cobra had the same part numbered gt40 iron heads as the 95 cobra r 351
Okay, this can get "challenging". If the 93-95 Mustang Cobra is on the same line as your car, you MIGHT be able to swap components. BUT, they are pitfalls. First, other than the heads, the engines would have to be identical. Same pistons, cam, all that good stuff. Same same same. At that point, the case could be made that the ONLY difference was the head, and thus you are duplicating a 93-95 engine, but not swapping a whole engine. Again, this would potentially fall under the update/backdate only if the cars on the same line.
Is this viable? Yes. Oodles of years ago I raced a 77 Civic in D/SP. If had what was called an EB2 engine. I found that an EB3 engine could produce some more power. My choices were swap an engine (could not afford that pre-internet), keep the EB2, or convert it. I had found that the ONLY differences were the pistons and head (put the EB3 pistons and head in an EB2 and you would have an EB3.) I sent a letter to SCCA with the documents and they said it would be okay. You will have to do the homework on your engine to see if you would be legal.