Power brakes acting silly!

I have a 1975 duster midly built built 340 in it and I've just got it legal and have been driving it around alittle. It has power brakes with discs up front and drums in the back. I'm also running a line lock. Me and dad bled the brakes and they feel great but as soon as I start the car they go to poop. When you hit the peddle it will stop but there's no resistance when pushing the peddle down. Even if you pump them it helps some but still sloppy. My cam is a lunadi voodoo with .513 lift and around 265/275 ish duration. I have a vacuume canister and I'm pulling my vacuume from the intake manifold. The manifold is an edelbrock rpm airgap. I don't have a vacuume gauge so I can't see what it's pulling. So my question is am I not getting enough vacuume? I've looked into a pump from summit. Anyone have any experience with them? I've also been entertaining the idea of switching to manual brakes. Is there a direct bolt on replacement kit for that? Any help or positive comments will be much appreciated!!