if they were working before you removed them, then don't damage anything and they'll keep working, installing new gauges is more likely to result in problems, you don't know the defect rate on those and it's not uncommon to find new parts defective .... the oil pressure gauge is the easiest, just hook it up and start the engine - being a mechanical gauge, it's the least likely to go bad .... other than leaking because you messed up the fitting
Bill
