I have the 79 - 292 inline 6 and the headers will fit.
Now if they hit the motor mounts just go on E-Bay [chevy 292]
and theres a spacer you can get for it. Stock screws wont work with the spacer..
I just took a hammer and dented one tube ..That worked fine for me..
Also if you go to a 4 BBL you will half to bump up your cam..
4 BBL`s tend to pump to much gas in there and the motor gets slugis if the cam is stock.
I just went thru all that on my swampbuggy.
I have learned that a holley 4 BBL 390 CFM is the best carb for the inlines to run with just over stock cams. E-Bay has them too. [Holley 390 CFM ]