If you're getting a pretty good stream at each of your 4 bleeders, chances are your M/C's OK. Just for the hell of it, how about adjusting your drums to almost full lock until you've found your problem. Also, make sure the pins that push the shoes from the wheel cylinders are not slipped off the shoes
Another thing you could check is how much clearance you have between the disc pads and the rotors when the brakes are released. If there is a lot of clearance, your calipers may be retracting to far and the pedal stroke is all used up before they contact the rotors. You could test this by sliding a shim between the pads and the rotors to take up the clearance and then try the pedal again. If it is better, then you may have the metric calipers that HemiRambler was talking about that are retracting the piston to far. I am pretty sure I have read a post here a long time ago about a residual pressure valve that wasn't holding pressure causing this problem as well. I guess having no RVP at all in the front circuit could cause the same problem.