No need to overcomplicate things by trying to make it too 'universal'.
For endmills and slot drills you need to be able to index around the 4 or 2 teeth so

a) make a disc to fit the spindle with 4 holes or slots to do the indexing and a spindle clamp that holds.

Next you need to control the movement longitudinally into the grinding wheel while allowing it to be withdrawn to prepare then fed in to make the cut but no deeper. This needs to have control to a thou, and be repeatable as you index round the 4 (2) cutting edges.

b) make your disc above true and concentric and be able to move it in to a screw stop that can be adjusted to a thou. eg a 40tpi thread with dial of 25 divisions. (see alternative later)

You need to set the cutting edge angle. Just go with 10 degrees and don't make it adjustable.

c) The simplest way to do this is to make a 1/4 inch metal plate that the is tilted by having a bar screwed to one edge to lift it up.

You want to traverse the cutting edge across the face of the grinding wheel although the first stage you can just screw your slide to the plate and do a plunge grind only.

e) fit a thin bar <1/4 in thick under the base of the 'thing' you already have at right angles to the spindle axis, such that it bears against the edge of the angled plate (c) and guides it across the plate at a fixed distance from the grinding wheel.

As an alternative to b you could put 2 screws through the bar (e) to bear against the plate which would then give depth control and tilt if you didn't remember to set them the same length.