Factory ride height doesn't make a whole lot of difference anymore with our 35 year old A/G Bodies. In most cases, every related part has worn, been repaired/replaced with after-market parts and/or altered in some way, changing that original spec. Still, the question, "what was my factory ride height" occasionally gets asked. In most cases just as reference point to start from.
Found a digital PDF file 1978 Chevrolet manual several years ago on the interweb. Under the suspension section the following page was found. The picture is of an earlier "A" Body and hoping they just used it for reference because of the then, model year design change. All the measurement are in metric so I'm assuming they were meant for the 78 A/G Body.
It's interesting to note that the lower controll arm ball joints and pivot bolts, rocker panels and axle to frame reference points were used in checking ride height for the A/G Bodies.
Steve
Found a digital PDF file 1978 Chevrolet manual several years ago on the interweb. Under the suspension section the following page was found. The picture is of an earlier "A" Body and hoping they just used it for reference because of the then, model year design change. All the measurement are in metric so I'm assuming they were meant for the 78 A/G Body.

It's interesting to note that the lower controll arm ball joints and pivot bolts, rocker panels and axle to frame reference points were used in checking ride height for the A/G Bodies.
Steve