Yea, I was told when my 340 stroker got dyno'd (426 cubes) that the intake manifold was at the head of the line in terms of choking the engine of air it needed to make more power and take full advantage of all the extra cubes, followed closely by the exhaust manifolds and the hyd. cam I chose to run.

Hogging out a cast iron TQ intake is no walk in the park! I guess if you did some hand porting, and had it extrude honed to the max you might get the best flow/volume one could expect short of sawing one into pieces, porting it to death, then welding it all back together.