What size bolts to mount starter?

I have a mini starter from Mancini. Its new but was purchased about 10 years ago. The bottom hole is the correct size and a 7/16 bolt fits through it right. The top hole measures almost 5/8". Has anyone run across this before and what is the best way to address it? I was thinking I could machine a special shoulder bolt or just turn a spacer to take up the slack.
Last question, does the stud go on the top or on the bottom?