I have 215/65R15 Tires on my drivewheels. I was thinking of fitting Mickey Thompson radials, Mickey Thompson ET Street® Radial (315/60R15), on the rear to get better grip. now as far as the size will it mess up the accuracy of the speedo since the speed sender is inside the transmission and will the car still be roadworthy with these tires? thanks.

 

If you could fit those tires to the car, then yes, they would affect the speedometer calibration. Now, why don't you start with aftermarket trailing arms, BMR torque arm, anti-squat brackets, adjustable rear shocks, subframe connectors, and some 275/60R15 M/T drag radials. That'll hook well enough to break your rear axle, then when you upgrade that, then you'll have enough traction to hook up an engine that makes enough power to lift the front wheels on launch, and break into the 9s in the 1/4 mile.
Fix the other stuff first, then worry about the speedometer.