Tony,
I believe that RAM also offered + engines, mostly for the 750, where it was "kicked up" to 22 lbs of thrust instead of the basic 17 lbs.
I had a basic 750 uprated to a + by Carlos along with an ECU upgrade by Bob Price. The unit's balance and EGT behavior allowed this upgrade. Depending on how each turbine performed in the test cell would determine their rating, either a 750, 750+ or 1000.
I understand that this criteria was also in effect for the RAM 500. Life expectancy was the final determinant with these upgrades.
I'm still operating a 750+ and a FTE-500 serviced by Bob and Carlos-both running well.

Art ARRO