need 3/10th

A 1/2 turn of preload while in the lower hole (front) is next to zero preload. Which could be why its bouncing in the water box.
The 1 1/2 turns others are suggesting is probably a good starting point.

Modifying the spring perches so that you could get into the upper hole is going to be your best move. Stick cars are very sensitive to suspension tune.
Going to a 9x30 slick, as 331mp says, will help greatly to take some of the "shock" out of the setup when the clutch couples. The Side wall of the tire will absorb that couple shock and keep the tire glued.
A radial slick ideally. Bias slicks grow and upset gear ratio in hi gear.
My cent and a half...