Just out of curiosity, do you still have the sticker/plate on the driver's door that shows the vehicle's build date? Be interesting to see how close it is to the number that looks like a date in the pic, might give some insight into how long your Jeep spent on the assembly line.
I can see why the other one reminds you of a part number, but if it doesn't match the part number for the unibody (does your guide show a part number for that, by the way?), maybe it's a production serial number for the body?
In my line of work, we assign numbers to hardware we build that are a combination of the technical drawing number for the part and a production serial number. If that's the case here, then part of that upper number identifies the the official design drawing of the body structure, and the rest is probably a production serial number for the part. Be interesting if someone else with an 88 could maybe take a look under their cowl cover and see what their numbers are? If the left part of that upper one matches (typically the production-order-unique part is on the right side for the numbers I'm thinking of), maybe I'm onto something. I may try and take a look at my '92 over the weekend as well - I don't expect an exact match to an 88, because there might have been minor revisions over the years, but now you've got me curious about my truck.
Also: I've never had an official build sheet for my Jeep, but maybe this is the sort of thing you'd need to confirm a "numbers matching" vehicle, in concert with the serial numbers of the engine/trans/etc., like they do with collector cars?