diampe: Don't judge too quickly on whether you need larger tires up front. I had some old 225F/295R 15s T/As on my ERA GT40. I switched to 205s at the front because that's all Avon ralleys came in unless I went to a much taller tire. On recommendation from Dennis Olthoff--Superformance--I elected to stay with the shorter, narrower tire, but was able to keep the 295s at the rear. The car was neutral with the old hard tires and remained so with the Avons albeit smaller fronts. I was able to pull much high g in the corners while remaining neutral with the Avons. Even was able to hang out the rear end by adding power coming out corners.
To loosen up your car, try a bigger rear bar. I like the sliding block setup to adjust bar stiffness. I've made several of these for race setups because they are great for making small adjustments.