Hi prd, welcome to Outdoorking.
This is the first I've heard of HD8s having serial numbers, let alone where they are located, so you have made an excellent start with your contribution. I'm aware that Greenfield's service department has very limited records that far back, but perhaps they can advance your mission if you make telephone contact. From what I've heard, they seem to be quite helpful that way.
Best of luck with this project - I will be very interested in the results.
