Before you start the flaming for the dumb question, hear me out. I bought my truck as a 1978 Chevy 1/2 ton step side. The engine is a 305 (which some on here have said they didn't think they used them until the '80s). The date on the engine, however, is 1977 or 1978 (can't remember which).
It has two fuel tanks, and a selector switch for both. Looking at year one's web site, they have the exact switch that is in my truck. However, they say it is for 1981 to 1987 trucks.
Also, when looking for body panels, I have never been able to find outer fenders for the bed that have square filler holes on both sides. All I can find for '78s are square holes on driver side, and no hole on passenger side.
Is there anything I can look for to determine the year? Most of the stickers on the truck have worn off, so I am not sure where to look.

Getr the vin number. It should be on the dash or on a plate on the drivers side door jamb (I have seen both on those trucks) Send me a PM and tell me what it is, and I can find out the year of your truck, and some other stuff.

I has been my experience that so much has been swaped around in most older cheveys that you can't tell exactly what year a truck is by the parts on it. As long as the vin # matches the number on the title call it whatever the title says.

Travis, I sent you a PM.
rcurrier44,
I just want to make sure I get the right parts when I order them.

305 was available in '78. The auxilary fuel tank didn't come on stepside trucks, so either a tank was added, or the box was swapped.

The tank switcher was used since '73. The later ones just had provision for switching a return-fuel line as well.

Thanks for the info. If they added a tank, they also had to add the proper outer fender (with the cut-out for the filler neck).

sounds like my truck. It's titled as an 83 but its either an 85 or 86. The grill config, dimmer switch and steering column, old paint color, wiper cowl, all point to 85 or 86. Vin reads as 83 but all teh door tags have been cut out and I wouldn't be surprised if a section of dash was welded in. Guy before me bought it at a sheriff auction in Texas

If you get the vin number the code is-
position 1 Division
Position 2 Chassis type c=2wd k=4wd
Position 3 Engine d=250 t=292 u=305 L=350 R=400 s=454
Position 4 Series 1= 1/2ton 2=3/4ton 3=1ton
Position 5 Body Type 4=Pickup
Position 6 Year 3=73 4=74 5=75 6=76 7=77 8=78 9=79 A=80
Position 7 Assembley Plant
The rest is the build number

This code is what GM used from 73' to 80'