the LR doesn't appear on the TCDS
A fine question, good sir. Will need to do some homework as I have not had any need to check the 727 against the TCDS. However, as I recall, the LR is referred to as the B727-200 ADV (ie advanced). Subject to a looksee at the TCDS, I would expect that the LR entries will be via notes with S/N applicability if there is no separate entry. As to what changes may have been made for the weight delta, that might not be readily available unless Boeing elected to put some words in descriptive text in the manuals. Comparison of the relevant mx manuals (to which I don't have any access) would reveal anything of note via a comparison if there be nothing explicitly stated.
Will have a look and come back later with whatever I can locate. The weight delta isn't overly significant - around 86T (-200) to around 89T (-200 ADV) as I recall - long time, now, since I have flown any of the models. I still reckon that the -100 was the pick for flying, though. A bit like a Super Cub on steroids.