AC Motor upgrade - pulley sizes

[birchy]

As mentioned previously, I am converting a Warco WM16 milling machine spindle from a 600W DC motor to AC with VFD. After much contemplation, I opted for a 1.5kW 2-pole motor. This was because I will be mostly operating in the 1000RPM to 3000RPM range and feel more comfortable running a 2-pole within its rated frequency. Although a 4-pole motor would give me better torque at low speeds, I would have to run it at 100hz (i.e. double its rated frequency) in order to achieve the top end speed I seek, which would reduce its lifespan.

I'm thinking of using a 5mm x 15mm wide timing belt drive rather than the existing gear system. The machine has a hi/lo gearbox with ratios of 1:1 and 2:1, which I will probably keep. So the belt drive would only be joining the motor to the gearbox input shaft. The current DC motor runs at 4600RPM flat out and has a 10mm shaft with a 20T brass gear. The gearbox input shaft is 15mm and has a 37T plastic gear. My thinking is that I can use around a 1:1 pulley ratio to give me a max speed of 2800RPM in HI gear and 1400RPM in LO gear.

Soooo...the main question is...what is the smallest pulley I can get on the motor shaft which is 19mm dia and has a 6mm keyway?

Or maybe one of you experienced chaps can advise of a better solution?