Note: picture of on-axle location of proportioning valve follows.

Stock brake pipe wasn't long enough; I cut and reflared it near the motor mount.
New line shown in photo was attached with a connector.

Adjustment - method was suggested with the car on jackstands:
to have an assistant lightly gradually apply the brakes while hand-turning a front and back wheel.
Start with 7 turns on adjuster; adjust to the point where front brakes just locked
and rears braking but still moveable.

Note on booster cars: as long as you're running a single-circuit system, the above method should be OK. On a dual-circuit system, only the fronts will be boosted. The number of turns will need to be established by experimentation, but will likely be fewer than without a booster.