Slant engines - 2 questions

Looks like newer than 72 engine but yeah they used to (factory Mopar) make a blockoff for that exhaust. Used more on small blocks than anything else I have seen. But you can make your own.
I'd bet the gasket for either the pipe or the block off is the most asked "what's this for" in a gasket set.
Cut that pipe you said you took off as short as possible and weld up the hole ..