Reading a tale from lathes.co.uk there was a fellow who fitted a 1/4hp 1400rpm motor to his Adept, no doubt via countershaft.

A larger motor will only give problems if you get a jam-up when working and the motor can overcome your jam. It might be able to cause more damage because of its extra strength. Perhaps make sure that your belt drive runs somewhat slack so that it can slip if it needs to.

If you want a new, relatively low-powered motor, i've found it is cheaper to buy a cheap Chinese-made small drill press than a motor alone. You often get a no-volt switch into the bargain, plus a chuck and a pair of bearings.

I have a Perris (precursor to the small Cowell’s late) which is abt the same size as your adept – driven by a 1/6th hp motor on a counter shaft to give 3 speeds ranging from abt 150 to maybe 450 rpm – obviously depends on what material + size you work with but also the head stock bearings – suspect uncontrollable with a direct drive from a 1hp motor