I can't speak for the 1993, but
ALL of the cab-mount bolts on my 1985 are 7/16-coarse.
If you don't know the secret, the fore-most two are impossible.
It has been a while; but, best I remember, those two bolts actually have one plain old nut, then hidden where you can't see/feel it is a threaded sleeve/nut thingie that is complete and total
PURGATORY to get off, especially on one that hasn't been molested since new.
There is absolutely no sensible reason for this threaded sleeve, except to hold a portion of the assemble together while coming down the line, until it is time for the rest of things to be put on; I threw them plumb across the holler, once I got them off.
