67 Brake issues

[graymond1967]

I have looked through the site, and have found some valuable information on brakes, but I am still not sure how to fix the problem.

The biggest problem is the pedal is hard and the truck stops, but not well. Cannot lock up the brakes at all.

1) 1967 C10 that came with a 327 and power drum brakes.
2) suspension was upgraded with 71 3/4 ton front disks, spindles etc.
3) rear suspension is now a dana 60 with drums.
4) The engine is an iron head 502 with about 15" of vacuum. My 1970 Nova has factory power disks, with about the same vacuum and I can lock the brakes up quite well in that car. So I am assuming the vacuum, while not ideal, should be adequate.
5) The manifold vacuum port has the transmission (TH350), gauge and power brake booster teed together.
6) There is a vacuum reservoir to assist with the brakes but I am not sure of the value.

I don't think the master cylinder was changed nor was a proportioning valve added. The reservoirs are equal in size and I am not sure if that is correct.

When I start the truck up, the brake pedal does go down as vacuum is introduced to the booster. So I would assume the booster is functioning.

I upped the idle slightly to about 600 rpm in gear and the brakes improved slightly.

Questions:
1) Do I have the right master cylinder?
2) Does the 502 have too big a cam and I will need manual brakes?
3) Do I have too much off of the manifold vacuum? I can reroute the transmission and gauge to a port on the bottom of the carb if need be.

Any other words of wisdom would be greatly appreciated.

Ray