well, the shims i have coming will be about 8" long. i can bellmouth it but the clearances i cant do much about becuase all this is hand cut. then again, 8" is way too long for this so i may be able to put a second shim inside and bring the clearances down even further. the problem lies in the fact that this is styrofoam and i need room to wiggle. for efficiency, is ir really critical that the propellers are situated a lot farther back under the lip?