I designed this mount to place the Makita as close to the z-axis as possible without sacrificing stability or making installation or adjustment difficult. This design uses the standard mounting plate from Allted. All of the other Makita mounts on Thingverse seemed to space it needlessly far from the z-axis, but after a little CAD work I was able to get a design together (blue mount above) that places the endmill only 45mm from the universal mounting plate, ~1.5 mm closer to the axis compared to the standard DW660 mounts (red mount above).
Additionally, I have found that most mounts on thingiverse seem to have little "wings" where the screws attach. This does make it easy to access, but it creates stress concentrations that will cause the clamps to fail prematurely. I tried to place the bolt holes in line with the tensile forces of the clamp to reduce any of these shear stresses.
9 x 6-32 3/4" machine screws
9 x 6-32 nylock nuts
M4 nuts and screws also work, but you may have to drill the holes out slightly.
I recommend a PETG filament. PLA might work for a while, but the heat of the router combined with vibrations during cutting will probably reduce its life cycle.
Use at least 4 perimeters. Higher infill is probably better, but it is these perimeter lines that are oriented to take up the tensile forces and are most important.