I'm afraid that by cutting the far side hole into a slot, it might allow the flange to warp. Taking the spring off the transmission, removing the left side mag cover retainer, & using the homemade wrench was the ticket to get that pesky nut off.
I plan to do some baseline runs w/ the carb before tinkering. If the fuel tube from the old carb will fit (and it has an extra set of holes like some of you have mentioned), I'll try swapping it back & forth before drilling any holes in it.
I got the carb unbolted last night but it's still attached to the throttle cable. I'll use a dremel cut off wheel to cut a slot in the twisted off screw to see if I can unscrew it.
Mike Sal