A 10 in swing is probably plenty.There are two versions of a Southbend 10 in,light and heavy.
The light has a small spindle bore.No 5c collets,no barrel through the headstock.The heavy 10 will use a 5c drawbar and has about a 1 3/8 or so bore through the spindle.
I see some so old they do not have quick change gearbox,I'd pass.
Subject to wear,and critical to thread cutting,are the half nuts.Be careful.
Old South Bend parts are available via Grizzly tools
Be aware of whether it is single phase or three phase.Phase converters are available to run a three phase machine.
The variable drive on a Clausing is great,till they wear and become loud and troublesome.Otherwise,a fine machine.
I like a 13 in Harrison.
Likely,the old South Bend is what you will find