BTW, our last 10 727-200s were the "advanced" model with, I believe, the Sperry 250. It would do a poor man's CAT three quasi-auto-land. It would flare but not de-crab nor provide roll-out guidance. We were trained on it in the sim but no one in his right mind would actually use it.
I worked a very large fleet of dual mode SP-150 722's that were just about all maintained to CATIII A minima. They were reliable, the most common problem with the 727 A/P was a result of elevator position sensors, caused alot of disconnects during autoland logic, porpusing, disconnects et cetera. I believe the a/b mode SP-150 would likely be the advanced mode you are thinking of.