got part numbers???
My kitchen cabinets have a 3/8 inset but Rockler doesn't carry those, only 1/4" or 1/2".link me...
up spiral cutter for the cut in a plunge based trim router...
you are making a small mortise that wants straight walls and not radiused...
make a clamp on stop which is nothing more than piece of ply cut to look like a ''U'' w/ the legs far enough apart to accommodate the router and length of cut...
add a leg to the ''U'' to form a ''T'' to facilitate better clamping and if you add a gusset for strength and stability to it you'll be ahead in the game..
the cut out for the stop...
make the throat a lot smaller.. and while you are at, make it a slot and not an open throat..
use a guide bushing on your router and let the router ride on top of the stop... now the router will be less likely to ''rock/tip'' as you cut...