The mast itself is 47' or the top of mast is 47' above the waterline? The reason I ask is that I was recently told I have the "tall rig", but see nothing in the owner's manual confirming that. I've seen a '79 Cherubini designed H30 with the chainplates attached to bulkheads rather than the steel tube, but don't know what it's mast height was. Always assumed they just changed the design for some reason between '79 and '82, but maybe the steel tube set up is associated only with the tall rig model.
Anyway, that digresses from your compression post issue. You have exactly the same compression post set up as my '82 H30 ("tall rig"?). Hopefully my sketch helps explain it. Sorry I don't have any idea how to replace that steel without tearing up the sole and a significant portion of the saloon. I hope it doesn't come to that for you.