It depends on the B body as to what size tire you can fit without cutting anything. 275/60/15's fit on almost all of them if I remember right.

There are fast guys running manual transmissions with radial tires but it requires more suspension tuning, clutch management (including clutch tamers) and fiddling than you may be willing to deal with. Bias ply slicks are more forgiving but if you've never driven a car with them before you need to be aware how they feel while driving, and it also will feel odd if you mismatch radials up front and bias plys in the rear.

If you dump the clutch on your 8 3/4 with slicks, it is going to eventually break. Slip the clutch on launches and you should be okay until you upgrade to a 9" or Dana. I broke pinions, u joints, axle shafts... you name it. You'll even break it with a somewhat sticky radial tire.