Mick do you have a trans brake?
If so try raising the launch rpm to 3200 it will HIT the tire harder. That was a good spot for me when I had SS springs, and then Cal tracs.

I also agree with MrP and Gregs dart. Do you have access to Dave Morgans Door Slammers chassis book?
Some of the info is outdated, but it explains moving the shocks and it's effect on the leverage.
That also effects the spring rate also.
If I had a scanner I would email it to you.
The placement of the shocks is very important in choosing spring rates.
Your car looks good, and that looks like a good track.
Don