Best advice I can offer is: measure twice (or more) and cut smaller than needed. I’m a carpenter and know how to layout and measure.
Long time ago I installed a set of Corsa exhaust diverters on my 23 Nova with a smallblock. I was super careful measuring and decided to drill only pilot holes where I determined the outlet centers would be. To make double sure, I went ahead and dry mounted the diverters and hoses up inside the hull. It was a big PITA but I’m glad I did it- because the pilots were both off by about an inch. After re-centering, all was good but it would’ve been awful if I’d cut the proper size holes. Lesson learned!
Good luck with you installation and post some pics when done!
