Brakes a bleeding nightmare

Help, I am having an absolute nightmare with the drum brakes on my series 3. I noticed the front left hand wheel cylinder was leaking badly so decided to replace both fronts and the flexis while I was at it. All done and then I couldn't get it to bleed. Got a reasonable firm pedal but the minute I got it off the axle stands and drove it straight to the floor. So I then replaced the master cylinder and the down pipe to the splitter. Have bled and bled it using a vacuum bleeder and an assistant and pedal still travels all the way to the floor. Have tried clamping the cylinders in with a ratchet strap and still no luck. At my wits end with the bloody thing

The manual is here and tells you how to bleed properly, what set up do you have , have you. Got the twin leading 11” drums on front

Clamping all three flexis is the place to start to find where the problem is , and go from there as in the manual
Did the shoes get brake fluid in them, have you got the springs on properly