Look for the H4 in Bosch or Hella. You're looking for these but the size for the four headlight grill.
http://67-72chevytrucks.com/vboard/s...d.php?t=615495
Look for 165mm or 4x6 H4. 4wheel parts carries them. $49.
You'll need to upgrade to relays and 12 g wiring but so worth it! Huge difference.
I run Bosch H4s in my '89 (the small ones) and I can burn the paint off the garage on high beam. lol