to the OP: Before you go to the trouble of tearing out the original mounting rails - I had the same problem with a CMP Hellcat with 615s. I eventually found that a small sliver (maybe 3/32") of fuel tubing between the plate and the rails at each screw location would "take up" the errors and even provide some shock-absorbing benefits. I have used this setup for several years and this plane weighs about 11-1/2 lbs. As long as I touch down on the runway (asphalt) and not the rough grass, I'm OK. The gear will work down to about 45 lbs. pressure with this setup. This is easy to try and saves the headache of removing the rails.
Good luck!
Jim