1996 mustang gt starter issues

Just dropped in a newer engine and transmission. Using all the same parts. I got the flywheel regrinded and bought a brand new clutch. The gears on the starter were a little rounded off but not much at all you wouldnt think it would matter. So I had put everything together and tried starting it. Once I turned the key it was making an awful screeching noise that sounded like it was coming from the starter. The pullies were moving a little bit but looked like it was struggling. I am afraid to try again because I dont want the flywheel teeth to get chipped or anything. What do you guys think? let me know if you need anymore info Thanks