350 starter problems

heres my problem...i have a 1967 jet boat that i pulled the 327 out of, its sitting in the garage to be rebuilt in the future. for now i dropped in a 350 and swapped over the starter which was a marine started i got used. well on the 327 it would always grind when the battery was low, just make a horrible noise. i dropped in the 350 broke in the cam took it to the lake and began breaking it in. got 2 days out of it but the battery wasnt getting charged so my trip ended. as the battery got lower and lower the starter really started grinding a lot. but when i charged the battery up to full it still ust grinded and grinded and i couldnt get the engine to start. but the engine ran great while the battery lasted. my to get to the point im about to buy a new starter, im just making sure does this sound like a bad starter? someone said i might need a shim but ive never done that before. the flywheel looked great when i tranfered it over, teeth were perfect no wear at all. but the started was always old and used.

lot of typing for an easy question lol i just havnt run the engine for 3 months now and i dont think i gave it enough time to completely break it so im worried i could cause permanent damage by letting it sit this long...