Gary,
If it's the HKIII-4035-500KV, then it changes everything on the ESC side. The motor Alan is running is the 4530-500KV LE.
Here are the specs for your motor: (As you can see the Amp specifications are far less on this motor)
Specifications
Stator Diameter 40 mm (1.57 in)
Stator Thickness 35 mm (1.024 in)
No. of Stator Arms 12
Magnet Poles 10
Motor Wind 9 Turn Delta
Motor Wire 21 - Strand 0.29mm
Motor Kv 500KV RPM / Volt
No-Load Current (IO) 2.02 Amps @ 10v
Motor Resistance (RM) 0.016 Ohms
Max Continuous Current 84 Amps
Max Continuous Power 3500 Watts
Weight 460 Grams (16.22 oz)
Outside Diameter 49.98 mm (1.97 in)
Shaft Diameter 5.98 mm (0.235 in)
Body Length 61.8 mm (2.43 in)
Overall Shaft Length 100.0 mm (3.93 in)
Max Lipo Cell 12s
Peak Current 104A (5 seconds)
Peak Power 4600 Watts (5 seconds)
Motor Timing 5deg
Drive Frequency 8kHz
For this Motor the Castle 120 you have will work perfectly.
Cheers,
Mark