Help me stop!

I would have said that using racing brake pads might be part of the problem, but went to the link and they say (unlike typical racing pads), these work OK when cold:

"Unlike most racing pads, your EBC Yellow Stuff Brake Pads have a strong bite even in cold conditions. You won't need to run a couple of laps before you feel the full fury of these brake pads."

The distribution block from your 1965 is simply a "quad T", all open inside, so can't restrict the flow. The 1973 one you had before was a "combination valve". You do need a proportioning valve for your rear drums and adjustable ones are just $30, or you can go back to your 1973 combo valve and get a prop valve, plus imbalance switch (wire to a lamp) and front "metering valve" (avoids nose dive).

As suggested, try an MC w/ a smaller bore, say 7/8"D, and insure you get all air out of the system so the pedal doesn't travel too far. There is a reason almost all cars today (w/ front disks) have power MC's, but many here use a manual MC w/ disks. BTW, any brakes - drum, disk w/ any MC should be able to skid all tires. Silly people here keep saying that drum brakes can't stop a car, yet they can skid the tires which is as far as you can go, indeed too far, you should brake to just before they skid or pump the brakes when they do skid.