Well, I fired mine up with the new FBO limiter plater plate set at the lowest level, 10* of crank advance and... it produced 16* with no vacuum advance. I had the idle set at 24* and it shot up to 40*.
There you have it. I'd say it doesn't do what it says it will do, with any kind of accuracy. Save you're money and weld up the slots to what works properly for your combo. I also noticed my fuel pressure is very low so I'm going to replace the mechanical pump now with a new Carter M6270 Super Strip that I have in the box. The AFR was going very lean at higher rpm. I'll get off this thread and start my own going forward. Just wanted to share my own findings, in case it helps anyone who might be thinking of getting one of these limiter plates. Mine will be available if anyone wants one. LOL