Diesel Dan is right , if you can locate a 292 manifold put one of those on instead of porting your 250 one. Porting is done by grinding w/a porting tool, electric or air type. Use a carbide cutter & just grind the opening bigger. I think you might get close to 2 1/4 opening?maybe???, if not that big, anything will help, I think it is smaller than 2" as they come stock?
Maybe some guys here have some 2.5" manifolds lying around??
