1) clean clean clean the outside of the engine before taking things apart
2) find a way to label parts and wiring, do not trust to memory, take cell phone pix of wiring connections, linkages, etc.
3) an electric impact gun works well for removing stubborn head bolts.
4) the intake can be stubborn, you may need to find a way to pry in the front or rear seam (that’s sealed with RTV) without doing damage (screwdriver padded with electric tape).
5) After removing the heads, take them to a machine shop for magnafluxing
6) after you get them back, clean the block deck surface and remove all old gasket material carefully. Measure warpage using a straight edge, it should be less than .003”
7) clean out the bolt holes with compressed air and solvent and clean the threads with a thread chaser
8) clean the threads on the bolts as well as you can, if they are too rusted, then replace them. I used APR bolts for the heads and intake
9) before installing the heads make sure each head bolt threads all the way in, if not find out why and rectify.
10) when installing the heads and intake use proper marine gaskets like Fel Pro
11) adhere to torque specs closely