1965 Valiant brake woes

When I got the car, it had a leaky wheel cylinder. When repairing that, we found a couple of bad/cracked drums. I spent WAY too much money on drum brake parts trying to get it working correctly. It also has some new shoes on the front. The brake hoses look new-ish, and aren't plugged or collapsed because we can bleed fluid through them.
The brakes have been bled to death. The last shop adjusted the proportioning valve and that helped a lot.

I still have mediocre braking, at best. The car pulls to the right under braking, even after adjustment. No, I have not had the shoes ground to match the drums. I'm not even sure if there's a shop in my area that offers that. The pedal throw is long and not confidence inspiring. It also varies ....soft at first, then firmer after driving. Pumping the brakes doesn't make a difference; only driving. I attributed that to building vacuum, maybe?

Now, I new issue has popped up. I can hear air/hissing under the dash when pressing the brake pedal. I'm pretty sure the brake booster has developed a leak. At this point, I'm not sure what to do. The whole system seems cobbled together by the P.O. I have no clue what pushrod is in there, what master cylinder that is, etc.

I've spent enough money on the drums that I could have converted to discs.

The easy and cheap answer would be to ditch power brake stuff and install a drum/drum master cylinder. This one is from Pirate Jack, but RockAuto has even less expensive options (though I would need some guidance on which one to get).

MC1323 - 1960-1970 MOPAR A, B, E Body BENDIX 2660809 1" Bore Drum Brake Mopar Master Cylinder

Since I don't know what all is in there, I should probably get a new pushrod too, right? Again ... I could use some help on choosing the correct part.
Then, would you keep the proportioning valve or toss it and put in a stock distribution block?

All of that work to have "stock" drum/drum brakes.

The more expensive solution is to go disc. Rip out all of the crap forward of the firewall and order a kit. HOWEVER .... I just had the entire front end rebuilt, so I would be throwing away basically new lower ball joints and needing another alignment.
PLUS, I have 14" rims and SBP. I would need to make sure my wheels even clear. The tires are like new. I really don't want to add in the cost of new wheels/tires.

Sorry, for the long winded post, but I really need some guidance here. I've spent a fortune already. It's not so much the money at this point, but I just want to do it right ONE LAST TIME.