Trying to figure out who makes these headers so I can call them and ask where to install my wideband. They look like 2 inch cmi but I can't find any part numbers that make sense.

They look more like Stelling headers to me. Brand really does not really matter. I'd have a bunge welded in this area
How to install oxygen sensor bungs. - Offshoreonly.com

My CMI's have 8 digit serial numbers stamped on the flanges that look just like that. I have been able to call them and give them the number and they can look them up.

Thanks guys. The wideband thread was excellent, that is what I needed to see

I will weld it up when i do my head and cam swap this winter, Going from merlin rec heads and the gm marine dual plane to afr 265 heads, merlin single plane intake and a custom Mike jones hydro roller. the head is a tad small to be perfect but i only plan on a peak hp on this engine around 5500, it should pick up over 100hp, more like 125. I also run the 850 flange intake and a hvh adaptor to a dominator, that set up will make more mid range power and torque than a dominator flange intake. I used to port intakes for reynolds racing out of seattle for there engine builder.

Why a dominator? IMO, no need for the power you're going to make and less tuneability on the low end and idle.

Agree ^^^^ 850 is probably big enough, might be giving up some low end torque with a single plane, and I agree on small head the as cast 305 AFR is a good choice

I have been on the dyno with 496 and 540 engines running less than 6k 0ver 20 times over the years and the dominators pick up power across the board everytime. Running the adaptor to a 4150 flange intake is key, it picks up a ton of air speed. right now with my 850 the engine is pulling 2 inches of vac at wot. Needs bigger carb. I can make the dominators run great with great manors.

I did a 509 chev few years back with afr 265 head and a chris straub hydro roller that did 690hp 680 torque with a dart single plane. once you get over about 510 cubic inches a dual plane just cant move enough air above about 3k rpm for these big blocks. and i am also building a package that will have massive air speed and torque less than 5500 rpm so the 265 will work good, my top pick would be the afr 290. But i have the 265's. I did a 565 12.1 compression with a solid roller and dart 320 heads rec port with a dart oval intake ported to match the rec head and a 1150 dominator that did 921hp at 6800 and 755 torque at 5200. That was also a 4150 flange intake with the hvh adaptor to a dominator.

I almost was going to bolt my 781 heads i ported, they pulled 630hp and 650 torque on a 10.1 496 hydro roller motor with a 640 lift 246 255 at 50 cam on a 107 lobe sep with a worked over 1050 dominator i converted to a 3 circuit.