1969 C20, brakes wont bleed after brake system rebuild

Hello all,

Hopeful that I will be able to write up a summary of my situation, and someone will be able to identify my mistake(s), or know of a diagnosis technique that will help me find my mistake(s).

I recently decided to upgrade my truck from manual disc/drum brakes over to a power disc/disc setup. After swapping over to the new setup, I was having trouble getting the brakes fully bled. Upon inspection, the lines were not leaking, but the line running to the rear of the truck appeared pinched(looks like it got bent too far and kinked by someone pulling on it). I decided that they were definitely due for replacing and bought NiCop lines, flare tool, bending tool and fittings.

Flared and bent all of the lines, making sure to have no kinks and deburring while flaring. I tightened all lines, bled master cylinder in car with provided loop lines, connected brake lines to master cylinder. I tightened the lines snug the first time around, but read online that tightening, loosening, tightening til snug and giving it an 1/8 of a turn helps to seat the joint so I have done that on every connection. Worked from the back left(due to the flex line being on the right side of the car that is the furthest from the master as the fluid travels) to the front left counterclockwise around the car.

I have consistently been able to get the pedal to work great after one pump, but never on the first application.I have removed the rear calipers to ensure the bleeder is the high point, put the disc between the pads and bled with it set up on my jack to ensure no air was stuck in the caliper. Attempted one man bleeding, traditional 2 man bleeding and vacuum bleeding. All to no avail. I used white teflon tape on the bleed screws to prevent sucking air through the threads and vacuum bled. When doing this I got continuous air bubbles, I am not sure what to attribute this to. My best guess is the threads still dont seal or my harbor freight bleeder leaks air in. Fluid flows as I would expect on every line. No fluid leaking at joints as far as I can tell. I have disconnected a few joints and seen a sealing witness mark which I also read about online.

What could I be doing wrong? How do I find the problem? Im stumped. Any information y'all could provide would be incredible.

Parts/tools used:

TGR Professional Brake Line Flaring Tool- 45 Degree Set - Single, Bubble, and Double Flares

Stop shop 3/16: NiCop Brake lines

Brake fittings: SUM-220137

Rear flex hose: RSD-FH112

Rear disc brake kit: 6772RWBK-5E

Master cyl/booster kit: MNS6772BB24 9B/1 1/8M

Oriellys DOT 3 fluid

TLDR:

Replaced master cylinder, brake lines, and swapped from rear drums to discs, brakes wont bleed fully. No visible fluid leaks from lines. Tried 2 man traditonal bleeding, one man bleeding and vacuum bleeding.