Noob with new ride

[ksjh1316]

[Hey new to the boards here just bought a 71 GMC long fleet form my wifes grandfather who was the second owner and had the truck for at least 25 years(he can't remember when he bought it). This is totally different for me as I am used to working on MG's infact I sold my current one to get this truck.

According to the build sheet in the glove box this truck came with and still has :

292 Inline 6
4-speed man trans code IM208D
Pos track rear end code IG80AB
P/S
Rear leaf springs
full cluster not just idiot lights

This is an original truck with 73k on her heck even the rubber floor liner and insulation are still in place and look good.

Only rust on the truck is both cab corners are starting to get soft. The bed is shot form it actually being used to earn a living for 36 years, and she still sports her original paint job in the glorious color scheme of White/Hugger Orange.

Can some one help me Identify the rearend and trans and to what they may be I am still a noob at American vehicles but want to learn.

As this truck is so original I dont really want to pull the 6 banger out is there a way to crank a little more juice out of her, or would changing the gears be enough? And what whould bee the best gear change to make if I wanted just faster off the line but able to do 80 on the highway. She crused home at 70 easily for the 2 hr trip but the speed-o is of by 15 mph gotta look into that.

For the short run she is sporting a 1/2 solid steel farmer made ram bar on the front and a 1/2 rolled steel rear bumper(before I fix her up time for some road rage lol)

I will post picks later when my wife gets in because she ran off with the digital camera.

Any help figuring this truck out is appreciated as just looking at the built equipment it looks odd.