I doubt the problem is the clutch.
I would start by pulling the shift lever and then take the shifter 'ball' (the part the lever is bolted to) out and see if it is broken. There should be a short lever on the bottom of the ball that engages the shift rails. My first guess is that might have broken off when you were in reverse.
If that is not the problem, then the trans might have to come out so you can pop the top off and see what is going on inside.
If it is stuck in reverse, can you engage any other gear? If you are able to, that will lock the transmission and nothing will turn. If you can do that then the shifter ball is probably ok and the problem could be in the shift rail for the reverse gear.
It also occurrs to me that the reverse/5th shift fork is on the bottom of the transmisson and is activated by a lever that is bolted to the driver's side of the transmission case. If the problem is in that linkage, then you should be able to shift into another gear and lock the transmission up.
BTW, I would NOT test the transmission lockup by engaging engine power. I would jack the rear end up and try turning a rear wheel or drive shaft.