Congrats on your new boat! I'm sure you'll love her. We have a 1970 P35.
The mast step is pretty straightforward, assuming it was the original issue I'm familiar with.
The inner face of the mast butts up against the outer face of the aluminum oval of the step and is secured with screws. The step itself is through bolted to the compression post below decks.
Ours had an iron pipe threaded or possibly welded into its center to allow cable routing (VHF, lights) to pass below.
When I took the assembly apart I found a fair amount of oxidized aluminum between the step and the deck, and the deck itself looked slightly depressed from the weight of the rig's loading over the years. I built it back up with some fiberglass and epoxy and polished the step, then used an aluminum protectant (Nyalic) to keep it from oxidizing again. Finished up with a whole lot of 3M 4000UV sealant as a bedder.
I've never removed the rudder though. Good luck!