I'd opt to shim the rear with shim stock,trial and error method,I'd start with .025 which may be to much or not enough.As to the screw length as long as 3 threads are engaged you have 100% holding power ,the rest are just extra is what I've been told by multiple machinests.You may just have to locate some longer screws of the same size and thread pattern if the shim required is quite large.