Hurst's current model Line Loc looks totally out of place on any period-correct car we might care about; do vintage units ever turn up for sale anywhere? I searched eGay and found zero results, even in the completed listings.
Gate a "Hill Holder" setup off a 50's Studebaker, it's basically the same thing. Push in the clutch pedal then the brake pedal. Brakes stay on when you let off the brake pedal and as you release the clutch it releases the brake. You can't do burnouts against the front brakes but you won't roll out of the staging lights.
Kelsey-Hayes used to make an electric/hydraulic trailer brake package that attached to the master cylinder with a tube. I have a unit that I plan to istall in my roadster when the build gets to that point. It's like a secondary hand operated master cylinder that mounts below your instrument panel. Requires a dual res m/c to isolate front and back brakes. Dan