RPO sticker is nice to have, but in that timeframe they were not very specific. My ‘75 lists the Silverado trim (nice to know, but no big deal) and Camper Special package (but there are metal emblems also) .
Nearly all the other key options on my truck are visible by inspection, even if the sticker was missing:
- Camper Special - Teepee emblems on the cab
- GVW - emblems on the truck, and data plate inside the drivers door
- A/C box and controls - A/C option visible, includes HD cooling
- 14 bolt FF 4.10 axle- not on the sticker, but the FF axle is easy to see
- G80 locking rear axle - can’t see it without popping the cover
- 350 4 barrel engine - visible, should also have a grill emblem in ‘75
- TH350 - just look at the pan shape
- NP203 full time transfer case - not on the sticker, but the shifter pattern (Hi-Loc, etc) tells all
- tire size - would be on the sticker, but easy to figure out if there is no sticker. Old tires may have used 16.5” wheels. Dump them and go to 16” wheel (from junkyard) and 245/75 R16 load range E tires if you want to keep it a 3/4 ton hauler. You can use standard light truck tires, but load range C tires can’t handle as much weight. You want/need tire height at about 31” with a 3/4 ton to keep the speedometer more accurate.