11A Cross-over exhaust pipe

Just completed one using the Franklin drawings and my original busted one... I used mandrel bend a of the right radius. The plans call for dull nickel plating ( not sure if I will do that) . I once had a cracked cylinder No 1 right behind the cross over exhaust. I remember Arnie pulling a piece or copper tube to listen to where the whistle noise was coming from. Was it just bad luck?

Any thoughts about insulating it with muffler tape at least behind the "radiator" , or would it be exaggerated. I do drive the car as many of you know!

andré