Last resort K20 '71 - hydraulic assist conversion?

[Murphy IRE]

I only have 11 to 13 inches of vacuum. I have replaced everything but the PV. The pedal depresses as the engine starts, but it is rock hard and stays that way, when I hit the pedal. I added an electric vacuum pump and canister, it helped but I still can't do an emergency stop. I was on gravel and hit the pedal as hard as I could and the truck came to a rolling stop (no lock up). I drive it in the mountains and I want to pull a trailer, but I'm affraid to.