Best to get a fastener kit like - http://www.oldchevytrucks.com/cart/product.asp?prodid=FP165&i=19294|||||

Many pop rivets are aluminum. You put aluminim next to steel and add a little moisture you get electrolysis and it will eat up the parts.

1951 Chevy 3600 rust bucket with GarWood dump bed conversion
http://www.flickr.com/photos/mikeybs51chevy