Oop's late on this one, you said it would be running this weekend and maybe wet. It does look really nice!
There is a ton of pressure relief info up on Boat Freaks & OSO, many of them are trying to keep it down around 20psi. They feel that the Merc unit is set to high at @30psi and keeps to much pressure in the system. Most any head gasket even the best will eventually weep, the fire rings keep it out of the cylinders but the out perimeters still weep into the lifter valley's and down the sides of the block. There are other on relief valves out there, another possible plus will be reducing back pressure in the exhaust. Did not notice are you running a strainer? You will need one to keep junk out of the relief valve.
Phil
No matter what your beliefs are "GOD BLESS AMERICA"
Fully retired marine tech near 60 years in the biz.