So I'll start with a quick visual comparison between the G0670 and South Bend...well even though its painted in hideous Grizzly green (Grizzly come on nobody is painting their machines green anymore) I say the G0670 wins the first comparison with its solid one piece cast iron base, vs the two piece base on the SB. I also prefer the black control panels, levers, and knobs on the G0670. The SB has a chuck guard...meh, the SB backsplash is curved...meh and pretty much everything else looks exactly the same doesn't it. lol
There are some differences under the hood. So far I found that the SB has a 7.5 hp motor vs the G0670 5 hp. The SB uses Allen Bradley electronics vs G0670 Taiwan, there are pictures of both electrical cabinets and they are different. Oddly both have a Yasakawa G7 inverter yet the SB inverter is larger hmmm. The SB has NSK or NTN Japanese spindle bearings. The G0670 doesn't say much about the spindle bearings beyond "Top Quality Bearings" noted in the catalog. The SB notes some components are manufactured in Japan and the USA, the G0670 looks to be 100% Taiwan. That's about all I have found so far. I would guess that if I could compare the inspection sheets for both lathes the allowed tolerances for the SB would be tighter. In any case I think the value proposition of the G0670 wins. If need be I could upgrade bearings and electronics at some point.
Here's what the president of Grizzly had to say about the G0670...