Nice Job on the wheels and tires!

Correct, they are hub piloted.
Therefore you do not want tapered lug nuts contacting the wheels. Two options, one is flange nuts. Other and the one I'm sure you should use is clamp plates with matching lug nuts.
Here's a picture, actually from a bred truck front axle...
http://rides.webshots.com/photo/2776297030080251109YhSQdn

They could then use tapered seat nuts to match the tapered seat in the clamp plates, but that does not make them stud centered wheels... some of the old clamp plates use flat ended nuts.

Another option along with the clamp plates would be to replace the 1/2" studs you have with 9/16" studs like newer trucks use, probably requires some machine work.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-