So you have only found the fuse box with the second rotation number so far? Still believe (based on what has been found on other SJ cars built same and other years) it is the rotation number.
Thanks Jeff,
Unfortunately, my car's original hood, rear valance, and heater plenum have all been replaced, so I can't check there. Most of the radiator support and front frame rails were also painted over long ago (and the entire car shell has subsequently been sand blasted), so no luck there either... I haven't found any ROT numbers on the seats either, but will keep an eye out for any markings when I re-upholster them...
How likely is it that the assembly line workers goofed up and put the "38" wiring harness in ROT "318"; or put the "318" rear-end in ROT "338"?
BTW - Here's a shot of the fuse box (please disregard the red carpet, it was only being used to make it a little more comfortable to crawl around inside the car)...