Thanks for the info - much appreciated!

As far as the iterative process vs. buying ahead of time, I'm just trying to get everything together to knock it out in one shot - I work an hour away from the boat and the fastener specialty store we have in town isn't open on the weekends - so I like to show up fully equipped for the full project if at all possible.

From Bill's comments it seems my guess (had to purchase the hardware a day or so ago) should work out fine, maybe a touch long but the solid part of the screw should be short enough. If it interferes with anything on the inside I can swap in a couple slightly shorter 316 fasteners and finish it next trip - I'll be isolating core through the mount holes ( instead of using 5200 lol) so I'll have that option.

Thanks again!