It should be fine if the circuits are the same, and you use identical tubes of identical age in each.
Used vs new Tube mono amp? - same model
Have a chance to pick up a used mono tube amplifier and pair it with a new Mono amplifier, same model.
Any concerns about sonic differences between the monos since they have different ages? Since it's older by about four years would it be better just to buy the second one new? Not sure how a tube amplifier ages aside from wear and tear on the tubes.