I have a top mount starter and a regular starter on 4 pt mounts, the lower starter is a bitch to change, but can be done on the river (ask me how I know) and the top mount, though easy to replace, has been unreliable, and is my 'back-up', only had to use it one time.
The 4pt mounts are indmar, I think (logs are, no name on rear motor plate, on same motor)

As far as the velvet drive bell, a motor plate between the motor and bell would set the starter too far back to engage the starter ring, so behind the bell would be a better bet.

Dan'l