Dude in the vid sounds like Don LaFontaine, the voice over guy.

When your done you want about an inch of clearance. Others can chime in but if it were mine, I would cut the stringer down and radius the top. place around 3 or 4 layers of 1708 cloth going 2 or 3 inches out on the floor on each side of the stringer to maintain the stiffness. Grind off the gelcoat in the work area.

Make sure that there are no sharp angle cuts. Radius whatever you do. If a sharp angle, good place to crack and splinter. As others have said, add glass mat on either side.

Makes me cringe when people say cut the stringer. I'm guessing it's too late to get another oil pan?

Yea. Much to late. It was just a cross brace. Took 1 inch out of it. Regal asked with mesh. At the very back of boat. It will be fine. It's not like I'm out in 8 footers. Even then it's rock solid

Structurally you are probably fine...I was thinking re-sale. Surveyor will pick up on the modification and flag it as an issue possibly killing a potential deal. Sounds like it's too late anyways. Good luck with her!!!