Slicks Size Question

Some of y'all might remember me asking a while back about a rear suspension kit for my 67 drag car...Well I ordered the Dick Miller kit, and have installed the new control arms, springs, and shocks so I put the rear slicks back on and was going to set it down to work on setting the pinion angle. Well, just as I thought might happen, the car now sits lower and the edges of the wheelwells hit the slicks.

The slicks I've currently got are M/T drag slicks, 29.5X15X10.5W, and one of them (probably both to be realistic) is just about shot. So, I'm thinking about new slicks already, and wondering about a little bit shorter slick. I think a 28X15X10.5 would fit, but I'm a little nervous about giving up traction. I'm assuming that once I've got the Dick Miller kit installed and tuned out traction should be pretty good, but would going down in size (shorter and narrower both) be a mistake? This car is a 1/8th mile car, and has run bests of 7.1X, has a 4.88 rear behind a TH-350, 3500 stall and a pretty stout 454. I've had some traction issues before but like I said the slicks have about had it and the previous rear-end set up left a lot to be desired. Any thoughts on this? Can a slick that size plant that kind of power/torque?

Alternatively, can anybody point me to a place to buy a spring spacer (one that goes above or below the spring, not a spacer in the spring)?