Arnie,
A 'GS31' prefix indicates a '2/2' variant Fairlady Z, Fairlady Z-L or Fairlady Z-T model made after the big update to Japanese safety and emissions standards in 1976. The 'S31' prefix indicated the compliance to the new standards, but it was still technically part of the S30 series.
Body serial number 010623 on a GS31 prefix would imply 1977 build year, and likely June to August build months ( you can cross-reference parts on the car for a more accurate build date ).
Engine would have been an L20 six with Nissan EGI injection, and NAPS ( Nissan Anto Pollution System ). Transmissions on these would have been either 4-speed manual, 5-speed manual or Auto, depending on model and/or chosen options.
Lots of interesting little doo-dads on these cars: Higher-specced models had electric windows, remote-adjust mirrors and 'eyeball' interior lamps etc.
If you plan the part out the car, you might get some interest from the HybridZ crowd as a parts donor for LHD to RHD conversion?
Oh, and I think the handbrake / emergency brake needs adjustment...!
Here are some S31 sales catalogue scans that you might find of interest:
Cheers,
Alan T.