Yep, it will be 1 1/8th.
That spec sheet linked above is really useful.
Good for spotting if original bits have been replaced over years with crappier things – like that chunky sadddle.
I would suggest getting shorter stem and slightly wider bars to give more modern look/feel. It’s easy to replace any of the drivetrain stuff – new cassette, chainring etc. Can also make it a 1x by removing big and small chainrings.
Weakest part of the bike is likely to be those old suspension forks. I switched mine for some rigid P2s off ebay. Brings overall weight down to around 23/24lbs.