Back in the 90s I ran a 68 Cuda FB @3550 lbs. Had big valve ported 906s that maybe flowed 280 CFM??? 13.1 compression 446 inch motor, Racer Brown 590 mechanical cam. Had a M1 with the newest (at the time) Holley HP 950. Car had a Dana 60 with 4.10 gears on super stock springs.
I ran this car for about 7 years and love to test . Car went faster with more plenum volume. Ended up with a 1 inch 4 hole spacer on top of a 2 inch open spacer. Combo went 11.teens @ just under 120 MPH.
Keep your porting money. Play with spacers or buy a Victor or TrickFlow.