I bought a Viceroy off of eBay about three years ago, then changed it to a short bed version of the same, and had a variable speed system fitted by local electrical engineers. This also allows for reversing the direction for a reading.
The short bed version has a tailstock which is essential for out of balance lumps.
I now have it raised on sleepers and braced to the wall, and it will turn big out of balance pieces. I can start very slowly to get them into balance and it will swing over 20” diameter.
It has cost about £800 in total.
I solved the problem of the mandrel size by machining the mandrel on my metal lathe, but this could be done by any engineering company, it’s not difficult, as long as the mandrel is trued up on the bearing faces. Then you can have whatever thread you want.
I love it!