I'll have to go pull the cam card, but by straight up I meant zero degrees advanced/retarded.

Essentially, yes, that is correct. They're a set of generic Bar BBC manifolds with a short riser. One of those, "this is what I had on hand" and don't want to throw a couple grand at an exhaust only to find out that it was wrong.

20 years ago it was running a cam quite a bit bigger than stock with that exhaust without any issues that I'm aware of. But, when you're in the boat business, everything is for sale if you know what I mean and I don't have that engine or the cam to reference. That engine had water issues one spring, so it came out, was fixed and sitting in the shop. Customer came in, "need an engine that will run with a 502, now!" and well.... buh bye. Dad sold it and the boat has sat shrink-wrapped for 20 years. After college 15 years ago I tried to beg, borrow, buy and steal it, but my father threatened to be buried in it. Took me six years to find a good hull that wasn't restored (wanted to build my own if you know what I mean), then an ex-wife and life got in the way. I started in earnest in Dec of last year and was then given my fathers boat in Jan, so now the one I bought is sitting shrink-wrapped waiting until... who knows.

I've been eyeballing the Seaward and EMI systems and I know Stainless Marine and IMCO also build good stuff, so I'm not sold on anything in particular. I'll measure hatch clearance, but suspect that +6 is do-able.

I would cancel the cam you ordered and put that $$$ toward good exhaust.

keep in mind that some of the after market heads ( AFR ) have raised exhaust ports, this will widen the gap you currently have.

Merlins I currently have already have raised exhaust ports, so I'm dealing with that already, but good point, thanks!

cam card tells you what it should be installed at. It doesn’t say what you actually installed it at. :thumbs

The last comp cam I degreed was off 3 degrees. I second questioned myself but after checking 3 times I was convinced. They were custom billet grinds. It’s partner was off 2 degrees.

my machine shop said advance cam 2 degrees.....
my cam card..
https://cimg1.ibsrv.net/gimg/www.off...6e74aed50a.jpg

I think I saw your card on one of my threads. Weren’t you propped for 5,500-5,600 if I recall. 548’s?? I’d think that cam would peak at like 6,300 or so (little less 2 deg adv).

i had a 731 in a 509, 5400 rpm fell flat, put a 741 in and 6000 no problem. cams were installed straight up. had a 420 mega-blower on it also with Bassett headers. 731 had a very mild idle, 741 had a nice choppy idle. And still idle at 800 rpm's just my 2 cents.