Yes as to the last sentence what is the max dinner plate that the current derailleur would support? If it could handle it I would be looking to put something like this on there:
https://www.sjscycles.co.uk/cassettes/microshift-acolyte-csh083-8-speed-cassette-1246t/
What is current bcd/tooth of the current front cog? I could buy a smaller one of that if need right if I don't want to get all the gubbins involved with the 2x. I never spin out that I can recall even on 28 smallest on my current bike. I just coast and wait to slow down!
I have never tried 1x so have to get my head around them. As you can see from this thread:
https://www.retrobike.co.uk/threads...-a-modern-drivetrain-on-a-vintage-mtb.484041/
I had this idea originally before people steered me away from it saying it would be too convoluted and better to go with 3x granny. However this bike of yours has fallen in my lap offering exactly what I was wanting to do on that original post!
Not bothered about purported chain retention benefits of 1x. Never found that an issue on 3x and besides looking for mainly road, but hilly, riding and light off-road.