Getting my *** handed to me.. these damm brakes

Do you need an adjustable push rod when you upgrade to a modern master with the 4 to 2 bolt hole adapter, due to the thickness of the adapter plate?

No. The offset bracket the OP is using is a different story. But a regular 4 to 2 bolt adaptor works just fine with the standard manual brake push rod. I have a stock manual brake rod and a 4 to 2 adapter from DoctorDiff, with one of his master cylinders.

I have and am chasing a similar issue. Air getting in. But no fluid leak out. I have read that this is possible with brake cylinders and/or master cylinder. Mine has the front disc brakes disk. And rear cylinder drum breaks. I read that it's possible the cylinder of either master or cylinder to move past seal protection that can allow air in. But once pressure is applied close to prevent fluid leakage? That this occurs using break cylinders or master cylinders that have been rebuilt perhaps one too many times?

I know it's throwing darts as speculation. But makes some sense?

It is possible for the master cylinder to leak internally. If the seals are bad it can create a situation where you never get a hard pedal. Like I mentioned earlier, I had a brand new master cylinder that was bad straight out of the box, no amount of bleeding solved the issue. I replaced it and everything was fine.

Now, whether or not that’s your issue or the OP’s issue is a different story. But it’s possible.