S-10 is probably the best for these trucks, but depends on the look you're after. Since the S-10 track width is narrower, you can either use wider wheels, or if you don't like that look you'll need to use wheel spacers.

Read here: https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=882889#Post882889

You can also do a search as there are many posts about this.

1946 GMC Pickup - S-10 Frame, 455 Buick, TH400, original patina.

My 46 GMC on Photobucket