It is much easier without the manifolds on. Mine was not too bad but was pretty tight. Note mine are SBC's. When I put them back I will be installing the outside manifolds once they are in the boat. I would take off everything you can to give yourself as much room as possible. Good luck!

Remove as much as u can, thats gonna be a u know what on thet boat, I think you have to remove the outside manifold lift a bit then the the inside manifold, or at least thats the best way I heard, we have several here (mopower) who are experts on this

I'm just taking my big blocks outta my 272. Had to take both the inner manifolds off but left the outside manifolds on. You can hardly get to the front mounts with the inner manifolds on. Took the power steering pump off as well, anything to make life easier really. Also best to remove your engine hatch completely and your ram. I also took out the rear bench seat as well so as not to damage the vinyl.

272 engine bay is mega tight so be prepared for a few bruises and cuts!!

The 454 Magnum is the 365hp. They also have aluminum intakes, 330's do not. Magnet test... The 365's also have all forged internals and rectangle port heads, good for any future upgrades.
Does your boat have sea strainers ? Change your water pick up hoses while engines are out.
By the way, nice boat and colors...Good luck

i planned on doing intakes with the manifolds. My buddy did headers and an intake on his single BBC, and gained approx 500rpm(330hp mind you) I was amazed to say the least. I know headers will flow better then any manifold, but one of the manufacturers advertises only like 13hp less then a header. So with that in mind and going with the stainless marine, Im hoping for 470rpm(lol jk). I would imagine some sort of gain, although I will not witness it as i plan on just doing everything prior to water tests. The manifolds apprear to be leaking externally, so I could imagine what the insides look like. Plus the fact the risers get untouchably hot idleing, so knowing that I can safely assume they are rotted/clogged w rust.

And i dont think my boat has sea strainers?? Where would they be located if so?

They would be located in the bilge under the motors. I think that with the external water pick ups you SHOULD have them. You may not but it would be a good idea.

If they're leaking on the outside, good chance they leak on the inside. After you remove them, pull the riser off, bet it's nearly clogged with scale. I had the same problem with a boat I bought a couple years ago. The previous owner ran the boat while overheating the engines because of no water flow from junk exhaust manifolds. I ended up rebuilding both engines and going with Stainless Marine exhaust. Great so far and I'm sure they'll be trouble free for years. Mine are trs and dry to the tips. Formulas are really nice boats, enjoy. BC

Get the serial #'s off the motors, you can check them or have them checked. The BAM website used to have some lined up by serial #'s.