Questions About My '62 C20

[Soupsdad]

Greetings, all. While going through a packet of paperwork from my old truck, I came across this. And now I have a couple of questions. What exactly is this document? And how unusual is it that it has a 261 in it? In my brief bit of research yesterday, it seems that the 261 was only available in 2-ton or larger trucks and buses? I appreciate any insight you all might have. Thanks!https://www.67-72chevytrucks.com/vbo...1&d=1654520428