Chevrolet: brakes 1968 camaro, piegeon forge, 1968 camaro

Question
i have installed a front disc power brake system on my 1968 camaro. all items for install came in a kit purchased at the piegeon forge tenn. rod run (new). i have bench bled the master cylinder and bled the brakes several time. cant get pedal to stay pumped up (no brakes).when they do get some pedal pressure,it wont hold as soon as you let off pedal completely.it (the pedal) goes back to floor on the next push.when you crank car and pump brakes there is no pressure at all. could it be the cam (488 lift with 232 exhaust and intake. i dont have a clue. could you help?

thanks for your time  larry silvers

Answer
Larry;
   When you are doing the bleeding is the car running ?
there should be the vacume line to the power asst. unit. bleed them with the car idleing and you should do each cyld 2 or 3 times and you must fill the master cyld. each time so it will not get any air in it. and start from the r/r than l/r than r/f - l/f than the cyld. too
just keep the mast. cyld. full at all times.  and there should be the line to the power asst. if it has one. ok
I do not think the cam would have anything to do with it.