the problem is that the wall thickness of the bushing will only be 1/32". most hardware
store brz bushings ive seen are cast bronze. These hold oil
better , that's why they us it, low wear but more brittle. You wont find one that has a 1/32 wall I dont think. Not sure... but you might find stainless steel
tubing around with .032 wall and 1/2 OD. a busihing must fit the width of the fork. I think it's best that your pin match the hole, but not convinced 7/16 in 1/2 is an earthshaking event. If the hole or pin wears, the load bearing side will then fit!. Not convinced there wasnt alot of that type of thing in the old old days. Still.... it's the head stay... probably the most important on your boat.
fix your screw up! It happens. Hard to get the chainplate off? The hole could be welded and reamed. I have seen pins with a worn shoulder on them that were in the right size hole... probably from rig pumping....