u can grind some flats on a sacraficial bolt to help clean out threads.
better,use a cutoff wheel for grooves.

(i wish spell check did corrections)!

 

The idea that the bolts might be a little trouble to thread crossed my mind, so I did give each one a shot of WD-40. Probably should go to a stouter lubricant.

Working the bolts in by themselves sounds like a good solution to get the thread cleared and then hang the bars with them afterward.

Thanks for the ideas guys.

 

i tried the single center hole,previosly not used, definetly very tight,i think gm did that to be sure they went in,AND stayed!
pix show used hole. i was curious about the work i did and never paid attn to the threads.
i dont think the bolts are too long,just 4-5 threads go thru the frame nut, maybe less