My recollection is that the "Custom" was an older fixed configuration Virtuoso with yellow brass 12" bell, no trigger, no gold trim, and (perhaps) a Cerveny valveset, that was marketed in the USA by Custom Music (of Michigan) for around $5,000 back in 20011-ish (around YEP-642S money). I would assume this was a Custom Music demo since I don't believe anyone else marketed a Sterling Virtuoso "Custom" model. If this has the Bauerfeind valveset, it is a particularly good buy, but it may have a valveset built either by Cerveny or a Chinese manufacturer. This horn should play with most (if not all) of the characteristics of any Sterling Virtuoso, and definitely would be superior to a JP234/JP374.
Doug
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band