Re: Mast Step Problem
Looks like you're missing another piece of channel that fits INSIDE the one in the hull, that would be hinged on that pin at the back end. What's odd is I don't see any holes in the block at the foot of the mast to pin it to the missing channel piece... Anyhow the two channel pieces would make a hinge that allows you to lean the mast back to lower it, and vice versa.
I've inserted the real link into your post so maybe someone's got more specific information. Good luck. A metal fabricator should be able to help out, or try googling "Rig Rite" as a resource.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)