Kinda tough to answer -
obviously a visual check of the cylinders for scoring and obvious wear (like a pronounced ridge at the top of the cylinders) Measure them if you've got the right tools for that.
How was it running before you disassembled? burning any oil?
I'd probably raise each piston to tdc and do a quick wire brush to get the carbon off - and blast everything out really good with compressed air.
how do you use the tractor? The heavier you use it, the more critical the answer here.
If it's a light/parade use tractor - you've probably got nothing to worry about if the piston's aren't knocking around the cylinders. But if you rely on it heavily... there's a lot you may want to check.