According to the 914 factory workshop manual when installing the front torsion bars the a-arm is pulled down with a pry bar to acheive what appears to be full "droop". I'm assuming this is to pre-load the torsion bar correctly once the ajuster is installed. Once this is done and the car is lowered with the wheels now on how much adjustment height (up and down) is possible. If for example after doing this you can't raise or lower it enough what is the correct way to correct the problem because the bar has already been pre-tensioned with the pry bar as mentioned.

I don't think there is a way to pre-load / pre-tension the torsion bars up front. All the adjuster does is change ride height.

I think if the a-arm was pulled to full droop then the adjuster installed, the front would be very, very high.

What I do (right or wrong, don't know) is:
With the wheels on, and the front of the car on the jack, pull the adjusters off both sides, then jack the front of the car to some point above where you want the front to ride. Put the adjusters back on, tighten the bolts an extra turn or so after the end contacts, then lower the car. Roll the car back and forth a few times to sag out the suspension. Repeat as necessary to get desired ride height. When raising/lowering with the adjusters off, I like to measure from ground to some point on the bumper so I have a frame of reference.