Ok, so it sounds like you have the original '63 GMC frame. Yes leaf springs were standard on GMC's '63 and up, along with a Dana 44 differential. All 1/2 ton trucks 1970 and earlier were 6 lug. Here is a recent thread about a '63 GMC gauge panel.
http://www.67-72chevytrucks.com/vboa...d.php?t=804330
There might be others found in the '60-'66 FAQ section