I used this 3/4 https://www.jamestowndistributors.com/product/product-detail/1586 for similar work on my boat.
It ended up slightly thicker overall that the old one... but then I had no concern being marginally thicker and that hidden area...
good luck ... hope you have a good vacuum pump... and working with a mask against gravity in such a cramped place... it IS truly exhausting.

Hope to see you in the water around Boston, soon :-)