If the stock motor cannot be rewired for 240VAC, not sure the practicality on upsizing the RPC, buying a step-up transformer and all the ancillary costs of the install. A new 5-7.5Hp 3 phase 230/260VAC 1750 RPM replacement motor can be had for $500-600, a lot less than the cost of a step-up transformer. If the lathe is not going to be used for heavy turning, use a 5 Hp motor and this will reduce the cost of the RPC or VFD used. A VFD would be less than a new RPC, but you could make a 10Hp RPC at about the same price point if you can find a local motor and add an RPC control box. With a 5Hp motor you can either go with a native single phase input VFD like the (Yaskawa GA50UB018ABA) or use a 3 phase input VFD in a derated mode (Hitachi WJ200-075LF, FUji, etc.) which run around $700.
Thanks. This may be the way I would have to proceed, unless I could find the right RPC/transformer equipment used at a good price.....and that could be challenging.