Centerline Convo Pro wheel issue

[40FordDeluxe]

My brother just purchased me a set of Convo Pros for my Corvette for my birthday! Today the fronts arrived and I noticed the hole opening for the wheel studs were fairly large and there was no taper. I was like WTF? I had spoke with Jeggs before we placed the order and they assured me the wheel center required a taper style lug nut. Cool, that's what I have now. I also asked about the rears as my wheels have holes for 5/8" studs and use a flat washer and non tapered nut. He had no idea. I called Centerline and they said my current lug nuts will work. Now, today when I call asking about the fronts, which isn't a big issue. They say the fronts require shanked lug nuts. But then the guy tells me the rear do as well. Uh WTF? The rears won't be here for another week and a half and their specs are that the holes for the studs are just barely bigger than 5/8" which tells me the wheel will go over the 5/8 studs. The tech advisor told me I'd have to either install smaller studs in my axles or return the wheels and buy some of their competition wheels. Yeah, not happening. He did tell me that guys still run the flat washers and nuts like I have but he doesn't recommend it. So do any of you have any experience with this issue? The guy told me they quit machining the centers for the convo pros 10-15yrs ago for flat washers. I have 2 friends that got some maybe 4 years ago and they were. I'm betting it will work fine, I'm just nervous.