I have a HI-Torque on mine, basically the same thing as yours.

They have to be indexed correctly. One installs the starter then measures how far the bendex teeth engage with the ring gear teeth and how deep the are meshed. You should have gotten some shims with the starter to adjust it correctly. If it is way out of wack the teeth could be binding and twisting the starter.
Could also be high compression and the engine timing, if the timing is so far advanced it fires the plug while the piston is still way down in the hole it could stop rotation or I suppose even push the piston back down causing the crank to reverse rotate and kick-back on the starter. That would only happen at low cranking speed, the power master should be turning it pretty good.

The starter it self has to be correctly installed on the mounting block. If it is somehow kinked over at an angle it could cause a binding. These are high torque starter due to gearing, if they bind something will break.

Or the could have made a bad batch.

I have a Ford style starter relay mounted on the fender near the battery. The battery cable to the starter is only energized when the key is in the start position. That also re routes the Start wire from the key to the starter and the R wire to your distributor if you have a points ignition. A jumper is attached from the S post of the starter to the battery cable post of the starter. When the cable is energized so is the bendex and presto.

I will post pic
large red cable is from battery;
small red wire connected to white fusible link connects to same post as battery cable. That is from alternator and charges battery and feeds system juice when engine is not running.
Blue wire is from start position at starter switch, used to connect to S on starter.
Black wrapped cable goes to starter, only has power when relay is closed
If I had a points distributor the wire that was attached to the R post of the starter would be attached to the same relay post the black wrapped cable is attached to..