Very interesting indeed. But how about if all you want is a street machine with some solid performance and a better mileage? What if you don't plan on taking it to the strip? Was the 518 acceptable?
Personally I don't think the 500/518 is a good option. While my car never ran hot, it did work harder all the time than necessary, and therefore I would stay away from this transmission. Knowing what I know now, I would much rather have a 3.0 ish (3.23 or the like) rear axle ratio rather than this particular 500/518 transmission.