Phil -- -- What I did was hang a rim that I knew was a certain backspacing/size on the hub/drum and went from there -- by looking at other tires that are mounted on rims u can figure how much wider the tire is when mounted BLAH BLAH BLAH and then get under the car with the known rim (or maybe 2 different offset rims) and measure how much clearance there is which direction the rim needs to move to make everything work -- from there you can guesstimate what u need -- u can always look at what others have done too -- It ain't rocket science .......... well maybe lol
Borrowed a big pair graduated calipers from the local tire shop...turns out I have 6's. That should make it easier in buying some street weight wheels.
After that maybe a pair of these...
http://www.mandhtires.com/store.php?crn=73&rn=311&action=show_detailAny recommendations as to tire pressures, street and race?