I use Allen Bradley drives and motors, 12.5Kw MPL-B motor on the lathe, 8kw MPL-B on the Beaver mill and 3kw F motor on the Bridgeport.
I have picked these up from eBay and you wouldnt want to buy new although quite a few of them were actually new. The price of the motor and drive that I have on the lathe would retail about £6000, I got them a lot cheaper, just over £400.
Now there is no reason that your motor and drive will not work and I suspect it may be due to you using the standard outputs on the G540 as I suspect they will be relatively low frequency outputs. I have not looked to see if there is any info on Geckos site about their max frequency though, so its just a guess.
Hood