Release the tension before loosening the nylon holders. I replaced the torsion bar on my hood two years ago when the car was painted. I don't remember where I bought the bar, but the right end 90 degree part on the new bar pointed in the opposite direction from the old bar. It points to the front of the car so all of the pressure inside the channel is to the bottom, rather than toward the skin of the hood. I didn't realize that when I first installed it, it didn't have nearly enough tension to hold the hood up.
I took the hood into a carpeted room and put an additional towel on the floor to protect the paint. It helps to have a friend help with holding the hood when installing and winding the bar.
When putting the hood back on the car, be careful of that S hook and the bar. If it gets loose, the unwind will not only scrape the paint on the edge of the hood, if your knuckles are in the way it'll break them with alacrity.
The nylon bits are available from Miller's, Bud's, the Benz Bin, and dealers. They're about $17 a set. Inspect the grooved cradle on the left side body as well. If it's too worn, the prop end of the bar could slip out causing the hood to drop too easily.
Ray
'68 280SL 4-spd Coupe