That's a handsome looking compression post (except for the very bottom). I'm curious what it butts up against at the top--looks to be a headliner--and how forces are transmitted down from the mast step shoe on the cabin top to the compression post. I assume that the bottom will sit on top of ballast or solid fiberglass that is covering ballast?
I would use some layers of 1/2" solid fiberglass from McMaster (1/2" because it is easier to cut) and build up epoxied layers. I would cut the bottom of the post off square, saturate it with epoxy, several coats. The new mast step should offer a tap in fit for the compression post and I would attach it to the fiberglass layers with a couple of 1/4" screws so that it cannot move (although since the post is screwed to the bulkhead you can belay what I said--it ain't goin no where).
The Bristol uses the U shaped door frrame of the head doorway as the compression posts...the two vertical frames of the door go down to transmit loads to the ballast. However Bristol does a very crappy job of it and it's one of the areas I will be shoring up when I get into the interior. I plan a similar layered block for each door frame--everything saturated in epoxy.
I like the work you are doing with the bulkheads.