Hi Paul,
That is exactly the wheel I have on the car right now, 15 x 10.5 with a 7 1/4" backspace.
I didn't use a kit to do my springs, I moved the front inside of the rail and fabbed a simple cup to hold it, then ran a couple of bars down from the cage to support it at the floor. At the rear I made a crossmember to hold the rear of the spring and used the stock shackles, here's a picture if the link works http://home.mchsi.com/~9secmerc/shackle1.jpg I'd do it again in a flash, it really wasn't hard at all. I had a chassis shop do the tub because at the time I couldn't figure out how to do it with the factory rail because it curves. They put the tub on top of the rail and welded a small piece of angle to bolt it to. I kicked myself for not figuring that one out myself, but I was thinking "in the box".
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Butch
460 powered 1967 Comet Cyclone (Broken)
10.271 @ 130.231
Butcher's Home Page
"Friends don't let friends drive Chevys"
[This message has been edited by Butch Jennings (edited 03-04-2003).]