I have a 1972 GMC Heavy - Half Ton with the 8 foot box. This truck came from Carleton Texas and has the Blueglass option in the cab. I have been told there was less than 300 hundred built with this option. The glass part No. is 1a1120 and I wonder if anybody could verify this for sure. I have been trying since 1971 and have not had any success.. It originally was a 6 auto but now is about 410 HP with 292 heads and a lot more. I have restored this truck to its origanal White and put Billet wheels on it. I love my Truck. Thank You