finding engine size
 

I'm new on here, iv'e been looking around serveral weeks.
My question is: how do I tell what displacement inline-six engine we have. it's a '68 GMC 3/4 ton (C20 equivilent in a chevy) I don't have the options plate on it.
any input would be appreciated :flag:

I'm not positive, but I believe mine had the displacement cast into the side of the block...

230s were rarely if ever optioned in pick-ups. Most got 250s or 292s. A C/2500 (GMC eq for Chevy's C/20) would most likely be produced with a 292 if it was an L- six. GMC also had some big V-6s.
292s are 1.75" taller than 250s in block deck height. A 292s side lifter panels are about 4 1/2" tall and a 250s are about 3". 292s have an asymetrical mount system. The pass side engine mount is forward of the fuel pump, and the driver's side mount is in mid block. On the 250 the mounts are even with each other in the middle and the fuel pump is forward.
Your VIN # will start out CS___ if it was originally an L-6, but it won't tell your displacement.

do you know where it would be stamped on the block? Also, it is not modified in any way, it has a 4 speed manual tranny; what kind of gas mileage can I expect?
Thanks!