Chakster mentioned Feickert in OP. Great device based on the Dennison Soundtractor, gets excellent results as long as it's used properly.
One thing often overlooked - an arc protractor is only accurate if your mounting distance is perfect (factory). If the factory is mounting an arm they didn't make, you might want to check it with a conventional protractor.
**Seems to me that a very slight error in implementing Lofgren A/B or Baerwald, or Stevenson, one that still results in two null points on the surface of the LP, is not going to make a huge difference in one's experience of the sound thus derived.**
+1 Although it depends on resultant nulls.
Chakster,
I bet you'll wind up with Loefgren alignment. Both nulls are within the recorded part of a 7". Error will be much less through most of song. Stevenson will be better at the end, but much worse up until there.