Has anyone experimented with 75-76 headers , turned backwards, into a single megaphone out the back? Basically running a dual exhaust ?????

Yes people have.

The engine benefits having both banks exhaust connected. Combination of firing order that benefits scavenging

I’ve seen megaphones with cross pipes that were better than megaphones

Thank you for the info. Do you know if the crossover was at the headers or the megaphones ?

Restrictive, and not efficient. This setup will actually lower your horsepower.

I suggest getting a set of 70-74 stainless steel heat exchangers and a good muffler to go with them.

Clay