Thats a South Bend, prewar...if I had to guess I would say circa 1911.
I used one identical to her (all lathes are women BTW), the shaft below is for bench mounting with a countershaft...back in the days when shops had powered countershafts running through them from an outside steam or electric motor.
She needs a lot of TLC before I would even put power to it, those babbit bearings won't take carbide speeds so stick to HSS. Hope you got the gears with it so you can change feed, kinda limits the usefulness without them. It needs a good cleaning, when adjusting the gears on the feed use a strip of paper to get the clearance right, those old gears tend to not run true on the pitch diameter so don't run it too tight.
A quick change tool post is nice but on these old lathes the carriage keeps the original post bolt so far from the spindle centerline you will need special holders for the tool blanks. With this lathe we just used the original tool holders and just inverted the cup under the post to hold the tool flat, you need to be able to reach out with the tool holder and need the length given with the original tool holders.
Don't go nuts with power, they don't have the rigidity for over 2HP...remember in the old days they used light cuts and slow feeds, flat belts slip at high horsepowers so even though the vee belt retrofit you have already is capable of transmitting more power don't do it.
My eye twitches when I see this old beauty because I spent more time playing with them than I ever wanted to, keep the spindle bearings well lubricated and adjusted properly (its shimmed), get it mounted straight and clean it up and she will turn lots of work for you.
BTW STP mixed 50/50 with 10wt mineral oil works great for a spindle oil and helps with vibration, we replaced the drip feed cups with felt wicks in the headstock to extend the time between lubricating the spindle...constant squirts from the oil can to fill the cup are a PITA once the spindle babbit is worn.
Here's a similar one.