Re: cable steering re-string
On the OMC stringers, the steering system was typically a push-bar through the transom (early models like mine) or tru-course which rigs to a gear at the intermediate housing. A '73 that doesn't poke through the outside of the boat should probably be tru-course. Good news is while that is an antiquated system ... it's a dynamite steering system.
I've not had to rig one of those, so I don't know what that means to you in terms of a cable. I've seen helms, gears and cables on ebay, but I don't know if you can buy new replacement parts for it. I'll try lookin' later if I get a chance ...