Here's the new motor. It's a 5 horsepower (3.75 kW) 3 phase, 240 volt induction motor (framesize 112M -- ebay $150).
My approach with this conversion is to use off-the-shelf industrial components as much as possible. Industrial AC motor drives are coming down in price significantly these days, and AC induction motors have always been cheap compared to their DC counterparts. This motor was manufactured in 1980 and apparently sat in a warehouse for the last 27 years, as it was brand new in the original crate.