[AlaskaK10]

On a 66 K10 rivet size was 3/8" hole size in frame was larger almost 7/16 to allow for rivet expansion. 3/8 X1 or 3/4 would be what you want the longer the rivet the larger you can buck the heads. I had planned on doing all rivets on my frame but at the last minute the company that was going to install the had a major failure in there rivet press and would delay my project for a period of time that was to long. I opted to bolt my frame together using 3/8 flange head bolts and lock nucts grade 8. Since 7/16 flange bolts had such a large head i made a bushing to fit in the 7/16 existing frame hole that reduced the size to 3/8". Kept the head size smaller and looks good. If you go the way I did make you bushings about a 1/16" smaller in height than the two frame parts your joining to allow for compression when you impact them togeter also use red loctite. The tube for the bushing I used was from Mcmaster car part # 89955K749
It already has a center hole that can be easily drilled out to 3/8"