Just put a new clutch in and torqued all nuts and bolts to spec but when I let the clutch out hard I get a big clunk underneath the car. I noticed the rear torque arm nuts were loose but after trying to tighten them it appears they are a through bolts since they just span without getting tighter. Does this need to be tightened up somehow?I don't know what else it could be...

 

Well after having a look at a diagram it looks like they are through bolts on the rear diff. I will give them a tighten and see if the problem persists. It looks like a common problem for them to come loose for some people.

 

What you're describing is common when you have a torn & separated transmission mount. If it was torn apart at the time you did the clutch, you would have noticed both halves parting ways. It is possible the mount was already split but not totally separated, and you didn't notice. Then giving it a spirited launch could have done it in. Jack up the tail of the trans slowly, and see if the mount does the splits.