I take it you have flipped (R-L swapped) stock cast iron manifold's installed, and have J-pipes to connect the side pipes. Factory five still sell the J-pipes for the MK1 cars but not the shorty headers. I'd call them to find the correct brand that will fit. There are several thread with folks having fitment issues with BBK, Ford Racing and others.
some examples:
https://www.ffcars.com/threads/ford-...itting.248813/
https://www.ffcars.com/threads/corre...-a-302.301640/
Its not the engine that is the issue, just accessories, motor mounts etc...