1970 C20 Disc Brake Swap - Vacuum Booster Question

[ScottN795]

I just finished swapping the front brakes on my 70 C20, however I'm having an issue with an extremely hard pedal and not much in the way of brakes. A quick overview of what I did: swapped the spindles for stock 72 Disc brake spindles, replaced the calipers with new stock 72 calipers (rebuilt from O'Reilly's) new upper and lower ball joints, new inner and outer tie rod ends with new tie rod adjustment sleeves, resurfaced rotors and new pads, new rubber brake hoses. I also replaced the M/C with a new 72 (rebuilt unit from O'Reilly's) for disc brakes. I also replaced the proportioning valve with a CPP not adjustable disc/drum unit.

The only thing I did not replace was the original stock 8.75" vacuum booster that originally was for the stock power drum brakes. I did shorten the rod from the booster to the M/C to the length it "appeared" it needed to be based on the throw of the new M/C, however it was really my best guess. I think my issue is the overall distance the rod is travelling into the new M/C is not correct, but I'm not sure how to figure out what it needs to be? I was also thinking of just biting the bullet and purchasing a rebuilt brake booster for a 72 C20 and just be done, (the 72" booster lists as a 10.81" unit) but that's another $100 or so and it's not a stocking item locally.... I have always believed that a brake booster is pretty much a brake booster (choices of single and dual diaphragm and bolt pattern aside) and I expected this to work...

Thoughts?

Thanks,
Scott