Thats the same kind of tires I have. They definately like to run in 1 direction.
Another thing that comes to mind is the toe adjustment. If they're toed out, it will tend to wander on the straights. try adjusting a little toe in, that should make it more stable. The more toe in you have, the less steering you'll have coming into the corners. With toe out, you'll have more steering coming into a corner at the expense of wandering more in the straights.
Also, check your rear toe in, make sure they're the same. I run most of my rear toe in at 2 degrees. Keeps my back end planted behind my front end.
I run most of my cars at 0 degrees toe, meaning the front tires are pointing exactly straight ahead. 1 of my cars though, my Mugen MTX-3, is very stable anyway so I run that one with 1.5 degrees toe out. Gives me more turn in steering so I can carry a little more speed throught the corners.
For foams, I like Jaco Nitro Shoes. 30mm rear 35 to 37 shore and 26mm fronts 37 to 40 shore. The shore rating is the hardness of the foam. Lower shore numbers = softer tires = more grip = faster wear. I run softer tires in the rear than in the front so the back sticks a little better. I can drive a car that pushes better than I can a loose one. Your own driving style will dictate which foams you use.
I always use servo savers, the stock ones do me just fine. There's always going to be a little slop in the steering, especially the older the car gets but you should try to keep it at a minimum. A little toe in will also counter the effects of slop in the steering down the straights.