Definitely more than cosmetic changes.
The weak point of the Arrow engine was the crank case. It would split down the middle of the bottom of it, and basicly it was just an awful crankcase. I think that was some sort of knockoff of an old Picco case.
Go engines seem to be the manufacturer of Arrow engines.
They might have picked up on the fact that the Arrow engines had a reputation of crankcase failure. Then they would want to "start afresh".
When I ran the Arrow engine I put all of it into an old Ninja JX crankcase (OS). I was happy with that, it ran pretty good.

The Go GX crankcase is a very solid crankcase, and I've never seen one fail.
So it makes sense to make this engine with an improved crankcase.

Furthermore all the new engines now seem to come with low CG heads. They've put a low CG head on this as well. I think that's a good idea.
So basicly they've gone with their concept, and improved it technically to be better quality/reliability and lower CG.

In terms of what it is, it's a nice engine, if you ask me.
Basicly a knockoff of OS VZ-B, an engine that people liked. I'd be tempted to get one if I found one at a good price.
The porting won't be the same and the crank is a bit more basic, but it has similar timing.

1. That's the nature of doing business.
2. Those distributors are likely to be the same ones that pick up this line of engine