[77 TRASHCAN]

I was thinking about this...
I sold auto parts from 1985 till 1998.
I don't remember seeing a system for a firebird 301 engine specific. I obviously have not ween everything. I was always looking at parts for my car (77TA).

If you insist on buying a system. The closest you might likely come, is to buy a system made for headers. Find a shop the can make down pipes. Have them made to attach to the header hookups.

A shop built system might be the best route. There isn't a lot of air flow through your 301, so 2-1/4 pipes may be more than needed. That size of pipe is much easier to bend than sizes above that, also.

I hope you find a way!!!