Semi-good high speed spindle idea?

I would like a high speed spindle for small diameter tools for my
mill which is limited to around 4K rpm. It would be nice if it did
not alter my x/y position and not use up much of my 8" of spindle
travel.

A right angle spindle where the motor is parallel to the table would
be ideal. It could be set to the spindle center and shouldn't take
up too much height. The problem is finding a decent high speed right
angle drive.

I think a solution might be to cut up a cheap right angle die
grinders. They are ball bearing, already have a gearbox, collet and
are rated for 11K RPM. I haven't looked but I hope I could cut off
the air motor and replace it with a pulley/belt attached to a high
speed motor.

Any thoughts, cautions or suggestions? I don't want ot sacrifice a
die grinder if I'm barking up the wrong tree.

Roger S

PS: I don't have a large enough comressor to run my vulcan spindle
grinder.