Definitely wouldn't try with a drill - if you slightly imbalance the clutch you will do everything from crack the frame rails, prematurely wear the bearings (clutch and driveshaft) and potentially put more strain on the pto side bearings of the new motor.
I would suggest ringing trident mowers in swan view
Otherwise a new 3/4 clutch half is $100. If you are dropping 450 on a new briggs or even more on a honda, 5/8 shouldn't be too hard to find.
