If you want to convert your wheels to use tapered seat nuts, there are steel inserts available for that very purpose. In fact, some cast wheels come with these inserts. Lug centric wheels are inappropriate for a car that's capable of fairly high speeds. Also, I'm amazed that PIM didn't supply you with centering rings. I can only assume they don't know any better. There are other reasons to have your wheels hub centric than making sure they're true on the hub. If you were to have a huge impact on a wheel, such as driving over a missing manhole cover, you want that impact to be taken by the hub, not the wheel studs. In such a situation, the wheel studs would probably just shear off.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.