Bob, I find the fastest way for me, to get past the pitting and staining, is to use 320 first. I have to accept that some bruises are just too deep to remove. Then 400. I find that 220 will get you into good material quicker, but the time it takes to get the 220 scratches out seems to be more work than just starting with 320. By the time I have gone around the flywheel twice I’ve usually had enough of it. I find that the 400 surface buffs up, on a buffer, fairly easily for me. I wet sand using a spray bottle rather than a bucket of water. I’ve done a few model A flywheels and the quality of the aluminum from the Lynite Company is significant better than their castings for the earlier motors.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.