Seems like it would be easier to install one of those after market units. There should be vacuume to drive the throttle unit found at the brake booster unit although it is at the wrong end of the car. I'll have to investigate.

The booster vacuum comes from the intake manifold.

Yes normally I would understand this but when the turbo is boosting wouldn't there be posaitve pressure at that point?

Yes, the intake manifold vacuum goes up and down depending on engine load, but there is a one way vacuum check valve that always retains vacuum in the booster circuit. Without it the brake booster wouldn't work.
Early boosters had the check valve mounted on the booster in the frunk, and later boosters had it back on the intake manifold.
Would be easy to modify the early system with an extra check valve in the engine bay to have a reliable vacuum supply there.

Sound like a good plan. Thanks for the advice.