Re: stripped thread in lower unit oil fill hole
If there's enough thickness in the threaded female portion of the housing you could try a helicoil. Otherwise you could drill and tap for larger bolt size then either place washers under the bolt head to fill up that 3/16 gap, or alter the head of the new plug so it fits down in the recess (grind down at machine shop or weld smaller head on plug so it matches the original). Given the usual softness of those housing castings, I think I'd take it to a machine shop and get their opinion.
1977 C&C 30 Mk 1 hailing from Port Clinton, Ohio