Each reef line should go from the sheave at the end of the boom, up through the reef cringle, and terminate on or around the boom at a spot slightly aft of the reefed cringle position. This will give the reef line a (admitteldy high friction) doubling and act as an outhaul as well.
The cam cleats built into the gooseneck will probably only "latch" with a significnt load on the reef line. It is possible the line's too large, but if you get the reef rigged in you may find that it cleats OK when loaded up. On a B51 I'd expect to see a winch to assist grinding the clew down and out when you're reefing.
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)