Looks like an Atlas 3000 series 12" lathe without the QCGB...nice lathes. The 3000 series were made from 1958 until Atlas closed up in 1981. Like all the rest of Atlas machines, they are very well made lathes that will last forever. Atlas lathes were denigrated by many as being "cheap" lathes because they made use of Zamak gears; which many wrongly called "pot-metal". Well here we are more than a 1/2 century later and all those "cheap" Atlas lathes are still going strong, Zamak gears and all.
I have two 10" Atlas lathes and I have ZERO complaints; they're solid machines. That late in the game most of the Atlas lathes did come with the QCGB but clearly there were some change gear machines still sold.
Does it have the change gears? If not, surf ebay for the gears and appropriate tooling for your machine.
Check out this web site for information on the old Atlas machinery...it's a fantastic web site; you'll enjoy it.
http://www.lathes.co.uk/atlas/page4.html