I hate to send someone to another website, but if you can find one on those other trucks, ask them how many splines the wheel has. Maybe someone on here knows or has one around and can count them for you, but you might have better luck there.
As far as the horn button goes, if it doesn't fit (and that's likely the case) then you can either cut- carefully- the two horn buttons and mate them together with some epoxy or resin cast a new hybrid one of your own making with one of those silicone kits you can get at the hobby store. You could also make a nice horn button cover and hide that ugly logo from the other truck behind a pretty IH logo.
http://www.alumilite.com/Hopefully someone on here with better knowledge than me can pipe in on how many splines the L steering wheel has.