Thanks for the advice, guys.
Home Depot actually had a board with screw ends on display, and I was able to find which one fit the motor mount and side frames. It was a #6-32, and as D500 says, I was able to cut them down with the dremel.
Now my FM is pulling better than ever. Took off like a rocket with four 70' cars. I still have the other end to do, and yes, next time I'll do what Dan says, as it was a little tricky to secure them by the round head for cutting. The nut will make it easier to clamp.
I also had to clean out the screw openings in the side frames with the drill to make the new screws fit.
Well, learning (and sharing knowledge) is part of the hobby.
Thanks again, guys.