Wheel adapters with the correct centerbore to match the hub and the correct diameter lip to center the wheel are superior to use because the stack (wheel + adapter) will be centered every time.
If the adapter centerbore is 70.3mm, then it will be located on the hub by the lugnuts. You might get it centered on the hub...but you might not.
When I've used adapters like this, it's not uncommon to have a vibration at a certain speed...maybe it shakes at 64mph, but it's smooth at 61mph and 66mph. It's annoying.
If you can find hub rings to make up the difference, that works.
I've used adapters from here:
http://wheeladapter.com/
http://www.motorsport-tech.com/
The first one used m12x1.5 studs. I didn't think the studs were very good quality. I chewed up a few and broke off a couple. On the plus side, the aluminum held up fine, and I just had to knock out the broken stud and pull in a new one.
2nd one, I specifically requested 1/2x20tpi studs. I also had them make the adapter with a longer lip to be sure it was deep enough into the wheel. My GM wheels had a wide chamfer on the centerbore.
Once the lugnuts are torqued, the clamping force holds the wheel against the adapter/hub. The studs are not seeing bending loads because you're not overcoming the friction between the wheel and adapter/hub. The centerbore is not needed to support the wheel / weight of the car.
100% weight transfer on 295 width Hoosiers on adapters. These wheels are centered by the lugnuts....the centerbore of the wheel is huge. Just make sure you torque everything properly and it's safe.
We used adapters on our 24hr lemons car with Corvette C4 wheels and I've tracked my 240 with adapters a few times. Additional brake heat hasn't been an issue. We never used loctite like some people...just torque the lugnuts properly.