Doc, great build !!! Best execution on this forum.
I had been considering using truck scales to weight my car as you have done. I wanted to share what I found out about how accurate these devices are.
The most accurate scale I found is manufactured with a 0.5% accuracy. That is the accuracy it has at shipment to its buyer. In operation accuracy is up to the scale owner, but the manufacturer recommends it be field calibrated over its service life to be 1% accurate.
So for a 3,700 lbs car, when the scale is on the manufacturer's floor the best accuracy possible is plus or minus 18.5 lbs. This same scale in the field after its first recalibration for 1% would be accurate within plus or minus 37 lbs. This info is for one of the most expensive truck scales made in Switzerland and its not likely we'll be weighing in on one of these anyway.
The most accurate American built truck scale I found has 0.8% accuracy at build time. Its operational accuracy is recalibrated within 1.6%. The range for this scale new under a 3,700 lbs load is plus or minus 29.6 lbs. And after its first recal that goes up to plus or minus 59.2 lbs.
Lastly would be the "run of the mill" truck scale. Manufactured for 2% accuracy and recal'ed in the field to be within 4% accuracy. That works out to plus or minus 74 lbs under a 3,700 lbs load new and plus or minus 148 lbs after recal.
Whatever type of scale used to weigh on, going back to it after a recal is likely a whole new ballgame.
What I'm looking into now is finding a shop that is setup to measure and adjust a car's corner weights. Hoping to find more accuracy in going that route but I don't have anything collected on this as yet.
My previous Camaros:
#5 - 2010 2SS/RS MN6 ABM #142-Silver Rallys-GFX / Med Titanium
#4 - 1994 Z/28 6M Black over Arctic White / Graphite-Red Inserts - traded
#3 - 1981 Z/28 Bright Blue Metallic / Black - sold
#2 - 1970.5 RS Mulsanne Blue / Blue - endo crashed it and parted it out
#1 - 1967 RS Butternut Yellow w/ Black Bumblebee Stripe-RPO D91 / Parchment-Black - sold