I have a Delta Shopmaster Drill press. I would like to reduce the speed
from 610 min to about 300 min rpm. Since this is basically an entry
level model my options are limited. I am not concerned about the
longevity of the motor.

Can a variostat be safely used to reduce speed?

This modification would prolong the need to upgrade models. The reason
I need a slower speed is to run a circle cutting tool from general to
cut neoprene gasket material. 500 rpm is max speed for this tool.