Yes, those over-the-door grab hangles use factory holes...and tiny little bolts. I have them in my 40 but I wouldn't trust them in a serious accident. I have ripped less than robust door handles right off their mounts in various non-cruiser related accidents. The handles on your 40's door are pretty dang wimpy in my opinion,
I have one of the Specter bars sitting on the bench right now. The Specter bars have 4 mounting holes versus most of the older chrome bars that everyone thinks are made of gold and have only two mounting holes. If you back it up with some big washers or, better yet, some 1/8" steel plate, I'd think you'd be pretty safe.