On MY 1975 37 footer....the upper and lower helm use a ROUND ROD...I believe the original may have been aluminum about 1 in long and 1/8 to 3/16 dia. I know it was fairly soft. I broke BOTH on my boat when I first bought it. The rudders were frozen and in the process of breaking them loose I broke BOTH. I replaced mine with aluminum hammer style rivets that I cut the head off of. The day I broke them I actually used a stainless screw with the head cut off to get me through the job. The shaft that the wheel rides on has a hole drilled all the way through it, not a normal keyway slot like I expected.
Its easy enough to pull the wheel off and check. Let us know what you find
Bill
1975 37' FB Sedan
Sleepless Knights
Bohemia River
Chesapeake City, MD