Here's a thread with numerous pictures of different 8 lug wheels and links to lug nut sources.
http://67-72chevytrucks.com/vboard/s...d.php?t=330740
As stated above, the aluminum wheels you are thinking about use dual thread lug nuts. These wheels were used starting in 2001 and would have used metric lug nuts. You will find several eBay sellers who sell the SAE threaded versions in 9/16" and 1/2". If your 1970 truck has the original studs, you'll need 9/16" nuts.
https://www.ebay.com/itm/32-LUG-NUTS...sid=m570.l1313