Clutch pedal stays on floor

The other reason the pedal may stay on the floor during a burn out is the engine is torquing in the mounts and you may be causing something to bind up in the linkage.

I had the same problem when I first put the 360 in my Barracuda and had two issues in the linkage causing the problem.

The mounting point on the bell housing for the ball stud bracket moved in 72 so there are different brackets for older than 72 and 72 up. This is not clear in most references. If you have the wrong one the z-bar does not sit level & perpendicular. When the engine torques it makes it worse and the pedal hangs on the floor. I had the wrong bracket and most of this issue went away when I replaced it with the correct one.

The other thing going on in my car was the clutch fork has a spring clip on the back of it the clips into a hole on the pivot bracket inside the bell housing. The one I had the clip was broken off. I had figured it was just there to keep things in place when you assembled the tranny to the engine. But, under hard acceleration without the clip the fork will twist on the bracket and hang up. Once I replaced the fork with a new one I have not had any issues with the clutch hanging up.