Hi, welcome to the Viking 28 group

Andrew Sensicle sent me an email asking me to respond to your question, as I am restoring a 1970 V28 that I found in a farmer's field.
It had a weak mast step and some wet, rotten balsa core in the forward section of the cabin top as well as many other issues. 
For the mast step, I felt that the original design was inadequate and decided to take the loads to the keel area of the hull instead of the cabin top.  I made the opening in the bulkhead oval by fitting filler pieces and an extra layer of plywood fwd of the bulkhead, all epoxied in place and then an extra piece of wood down either side of the opening from top to bottom to stiffen the bulkhead.  I attach a couple of pics to illustrate.
I don't think the metal parts will increase the stiffness much because it is not oriented along the load path, and it looks ugly.
I have built several boats over the years and have a business doing custom yacht services, but this is a labour of love!

Please email me if you need input.

-- 
Roger Jubinville
MLC Services
Toronto Canada