"Working on a 40 wagon"
You could get a more relevant answer than this one on the 'Early' pre-'54 forum, at this link...
https://www.fordbarn.com/forum/forumdisplay.php?f=4
Just in general, and baring any clearance complications, tapered fittings or enhancements like cotter pins & self-locking nuts, I think that a nut should be below the bolt if possible.
So if the nut somehow falls off, the bolt still has a passing chance of (loosely) staying in place, instead of more quickly falling out.
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