Yes, wheels can get confusing, as there are many different types. It really comes down to how the wheel is piloted to the hub. Some wheels are stud piloted, meaning that the studs are what aligns the wheel and the center hole doesn't do much. Usually, they have a very loose fit to the center hub. Then there's the hub centric wheels. Those will have a tight fit to the hub, as it is what centers it. Most larger trucks as well as many late model cars are that style. As to what supports the weight, it's a combination of the components, the studs carry the weight by way of the nuts. The nuts will support the weight through the taper seat in the case of your wheels. Once torqued correctlly, they should support just fine. As to the 7/8 nuts, it's the larger seat that we're after, as the wheels you're using were made to run with the larger nut. The hex size really doesn't matter too much, as long as the seat is large enough.
On mine, I'm runing the '73-'91 Blazer Rallye, which was originally intended for use with 7/16" studs. The 1/2" studs clear fine, and the nuts worked well. What happened inmy case was that I came across the late model caps, and really liked them. The vendor also had the nuts. I did have to modify my wheels a bit by enlarging the seats to accomodate the larger seat diameter. I accomplished that by using a 3 flute 60 degree counter sink bit (a really big one! ) and working slow to get the size. I wouldn't necessarily reccomend anyone doing that, though. In my case, I have experience doing that repairing damamged wheels at work. If you would like to see what I've got, click on my signature, it will take you to my pix.
