Stuck Heat Riser

I removed my slant 6 exhaust manifold and it was stuck over half way closed
I did everything you did with no luck at all ,that 66 heat riser was there to stay...
I had a friend cut it out from the inside with a metal blade on a air driven sawzall.
I did not want it in there any way, it is to help get the engine up to temperature and living here in Arkansas with a manual chock I did not need it to restrict my exhaust
We was going to use a torch and heat it but no gas..... I still have the manifold if I ever go back to single exhaust