A magic gear is what you need.
This is the gear combo that means a chain will just fit with no tensioner and the right amount of tension.
Been running an SS old marin for years with no problems.
Measure the distance between the dropout and the centre of the BB and google magic gears where you will get a calculator to give you an idea.
Chain stretch is an issue – a new chain vs an old stretched chain is worth one link.
For my marin, a new chain would be tight with 34*16 so a little over geared, after a week of riding tesnion would be perfect.
After a month, chain would be baggy and I could get a 17 in there to give 34*17 in there which would be perfect.
Any questions let me know.
Cheers
J.