Rob. I think .003 feeler gauge is gonna be impossible to fit, just use a piece of .0032 newsprint per the milodon installation page. Use a strip between all 3 gears, push the idler in tight and tighten ( they use a small tapped bolt floating in a larger bolt hole in the plate) to 35 ft/lbs as the center idler is retained on a plate. If you could mount that idler on said movable mount plate then you could move it and tighten. If space does not permit that, maybe an eccentric type bolt with an offset bushing so you could turn those and get what your shooting for backlash wise. Per Milodon:
".....You can now proceed with the backlash adjustment. Use a single strip of newsprint (not gloss magazine
paper) 1/2" wide x 6" long, and wrap the newsprint around the idler gear, between the cam gear, idler gear and
crank gear. Press the mounting plate and idler gear assembly firmly by hand toward the cam and crank gears (this moves idler plate in) , being
sure the newsprint is in place. This centers the idler gear between the other two gears as well as sets the lash
between two pairs of gears all in one procedure. A dial indicator while appearing more high tech, can not
accomplish all these procedures. .006-.008 on each set of gears....? Not sure how you check between gears but I got my LA set up so there was .007 cam play against a stationary crank. Am I supposed to have 6 to 8 thou X2 at the cam gear? It's adjustable with 3 bolts (1 moves, 2 just tighten) so im not stuck with a bad drilled and tapped hole.