A500 was based on the 904, A518 was based on the 727. I don't remember the exact year they switched to the fully electronic (becoming the 46RE), but I believe it was around 1992. They also made 2 versions of the A500, the 42RE and 44RE. 42's were found behind the V6 and 44's were found behind 318's in the Dakota's and possibly some Rams.