Generally residual valve would be inside the front fitting on the master cylinder but I really don't know. Could be in the prop block. I don't know the specifics of the '69 B. Someone else might and the remanufacturers ought to.

There's some good factory technical service information at the imperial club. Scroll down to 1969 and check out '1969 Service Hightlights' for the brake changes instituted that year. Then check out the other brake specific bulletins.

Let me get this right, the car has the 10 x 1.75" brake drums on the rear or the wider ones?
In either case, they should be stopping the car at low speed. The wider ones would be better but whether 11s are worth the wieght is questionable. Bigger brakes will help dissapate the heat but there is no heat being generated so that's not the issue. Most lining materials work better as they get hotter but they all have optimum ranges. Street linings work from dead cold (even in the arctic) to at least a few hundred degrees. Race only compounds work from from a few hundred degrees to glowing hot. So those are the extremes. In the repeated high speed braking that occurs on a road course (or an oval) a lot of heat is generated and needs to be removed.

No rear bar at this time. Unless you've shifted a lot of weight to the rear, this car needs more front roll resistance. Adding a sway bar to the rear will increase the rear roll resistance that already is relatively high compared to the front. As a result you're getting into the possibility of oversteer situations developing at high speed. There was a discussion on oversteer not long ago in this forum - search function should turn it up.

Well I know tires (and wheels) are not cheap, but you can play with ride height that way for sure. I use a a 'tall' 70 series tire on the street (actually close to stock diameter), and a short 50 series tire on bigger rims for autocrossing. For the time I did a rallycross, I cranked up the t-bars a bit and used the street tires. One advantage of smaller diameter tires is you may save weight.