Trouble with brakes

[J-Rod67]

thanks for checking my post. I am having a lot of trouble getting my brakes to function properly on my 67. It has been converted to power disc brakes and m
I have tried countless times to bleed the system and get the same results each time. I have replaced all components with new ( lines,calipers,wheel cylinders,mc,booster, prop valve). After bleeding each line until all air is removed I crank the truck and test brakes with no success and then discover air in all lines again. This happens every time. After another attempt today I noticed that the front driver side will not bleed (possibly air entering at the bleeder?). Can this one wheel cause air to get back in to the whole system? Anyone had this much trouble with brakes and have any suggestions? Could the prop valve cause trouble? Any help would be greatly appreciated.

Thanks
Jared