"I've also seen another 'mycnc' contributors hardinge powered this way, and it's impressive. It also makes sense to me as it retains all the original lathe controls."

Not sure if it's mine you saw but if so thanks! Mine's written up at

HLV conversion to VFD - circuit and pics

Six years on it's still working fine. If I were to do it again I'd probably somehow add an interlock to the speed change as various people suggested just to be on the safe side and also an external speed pot. But neither is likely to rise to the top of the projects list for a while.