The rowlocks do want to be as far outboard as possible – but the gunwhale construction does limit this. Ones I have seen tend to be eccentric on the wooden pad.
The problem being that the oar will tend to foul the outer edge of the gunwhale – this depends on the length of the oars and to a lesser extend the rower’s technique. Raising the rowlock can help – but then may leave a bit of a lump for the crew to sit on when sailing.
When I fitted out our World I drilled a small hole first – to be sure the position was correct.
Everything should be tied on or secured to the boat in some way – especially if it does not float. On rowlocks, either the small eye in the end, or a snug line around the neck. Have the lanyard long enough so that the rowlocks can be unshipped and sit snuggly somewhere without detaching the lanyard.
BTW rowlocks do come in different diameters, so make sure you match them against the oars+collar diameter. The idea being that the oars will not lift out of the rowlocks when you are rowing. The oar has to be placed in the rowlock where it is thinner. You should not have a problem with the rowlocks lifting out of the sockets when rowing.
PS Galvanised are perfectly adequate as far a strength is concerned.