Rear Shock Length?

[53lowdown]

62 C10 SWB, Anyone know what the stock rear shock length is when sitting on the ground? Mine had shocks on it that were 18.5 in maximum length, but when I removed them, the truck bounced up about an inch. That explains the jolting ride. It almost looks like the frame mounts for the shocks might have been moved back on the frame - the shocks sit at about a 45 degree angle. I'm just wondering if ordering stock shocks will fix it, or if I have to look for something longer, or move the shock mounts.