Ask yourself a lot of questions first......
John:
You have already identified my major concern for restoring vintage lathes as a "user" lathe.... the spindle size...
The non-standard spindle size will continue to be an impediment to adding chucks, faceplates, and other accessories to the lathe. I suppose you could have a special adapter machined for this threading to a standard size, but you will need to use it at all times to fit currently available accessories.
You also do not state if there is a Morse Taper present in the spindle - the vast majority of present-day taper accessories for wood lathes of the scale we normally work with is a Morse number 2 taper. (Also, a similar concern exists for the tailstock quill - the taper size and operation of the quill should be checked). What size is the tool-rest shank? [Modern tool rests tend to standardize on 1 inch (25 mm) in diameter.] Another thing to check is how the banjo and tailstock lock into position on the lathe bed ('ways') - is this a bolt-based system requiring a wrench, or is there a lever/cam locking system?? The convenience and speed of such an adjustment system needs to be considered relative to what is available for a modern lathe - the more difficult or inconvenient it is to make the adjustments, the fewer times you are inclined to move the parts!
Other obvious questions are to examine cast parts for cracks, check mechanical function of all parts, and evaluate the motor and how specific it is to that lathe. If the motor 'craps-out' or "dies", can it be replaced easily, can it be repaired/re-wound, etc., or are you dead in the water? Fears of having to find a unique, lathe-specific part are always present when restoring or using a vintage machine.
I have known people to go through quite a bit of effort and expense to bring back a vintage lathe 'to life", only to be frustrated by the inherent limitations of the lathe's original design compared to 'modern' lathes available today. You will have to answer the question of whether you will be able to live with this lathe for a while, invest the time and money into its restoration, and are willing to take what may be a loss if you intend to sell it in the future. There probably will not be a lot of buyers for a lathe of this vintage, even if nicely restored, other than those wanting to own something vintage (which will likely be few in number). It would be good to ask yourself many of these questions before making the commitment to buy and restore a vintage lathe as a 'user' lathe.
I love to see vintage machinery restored, but if this is to be your primary lathe, I would be hesitant to take the plunge. Last year I restored a very small treadle lathe from 1881 (maybe the first 'mini-lathe' - a "Prize Holly" Lathe made by A.H. Shipman in Syracuse, NY), and enjoy it as a "looker" lathe that now sits in my living room as an antique. I enjoyed going through the restoration process, but I don't think I'd consider restoring a vintage machine as my main "user" lathe, given the concerns raised above.
I hope I've given you some food (and concerns) for thought...!!
Rob