[Art Burtt]

It sounds like body is hanging up on something. When I put my body on I had to slide it slightly forward and then back so the defroster tubes touched the cowl bar. The back where the body sits on the frame was off by about a 1/4 inch so I shimmed it.
The body should fit down inside the frame rails on the inside.
The book says use the self tapping screws to fasten it to the frame. Don't do that ,drill and tap for 1/4 in. bolts. Leave the bolts loose so you can adjust body so the doors fit right. Make sure you have at least 1/4 inch around the door. I tightened them up with body filler on the body to about 1/8 inch cause I thought it looked better. I had to widen the gap to 1/4 inch cause the doors where hitting when I went over a bump and the car flexed. Make sure to check clearance of the hood hinges in front before you drill holes and bolt the front of the body to the frame. Just make sure you have enough clearance so the body doesn't rest on the hinge mounting point. Are you using springs or coil overs?
If springs check the adjuster holes.