if your data plate is missing or worn off it's anyones guess as what the model number is
as for the location of the serial number generally they were located on the RH side of the frame, around floor plate area either at the floor plate or along that side of the frame. Also another location is along the hood where it meets the frame. This looks like an older machine so it's probably along the side up near the floor plate area. (those serial's started with an N followed by numbers).
If the truck has been painted you'll need a scraper and some cleaner most likely.
From the pictures you posted it looks like a GLC050RC or RD model, i'd say and RD or maybe an RF. If this is the case then the serial number would be the newer format with the 10 digits as opposed to the older format of 7 digits.
That's a D5 engine for sure, triple stage mast as previously mentioned. Unfortunately those tags you showed are standard tags required by osha on all lifttrucks, they don't tell us much on the model number.
If you do find the serial number it's the letter on the end of it that designates the year of mfg.
Pre2000 those serials were 7 digits and started with a N. The year of mfg was determined by a letter in the model number i think.

Post 2000 they went to a 10 digit serial number and the year designation was determined by the letter on the end.