I didnt personaly find the left handed screw to be tight at all, Try an impact driver, if not - as James said- drill them out.

An impact driver is like a screw driver but you hit the top of the handle with a hammer and the force turns the screw driver bit.

I use 30amp electronize with exsternal relays. I run my motors on 21v so if you use urse on 12v you wont have any problems.

If leos speedos can handle the current you will be fine.

Wheels can be bought from Ewans shop to fit the drills, I suggest the 75mm blue wheels, with 3/8th UNF nut inserts- Its what i use and havnt had a problem.