I would be leery of switching a high mileage engine to synthetic at that stage in its life. Several years ago, my daughter had a high mileage Fnrd Probe. It had noisy lifters, but used no oil. Mobil 1 quieted the lifters, but it immediately began using high quantities of oil. Returning it to the same oil brought back the lifter noise, but the oil consumption continued. switched to Valvoline MaxLife and the lifter noise lessened as did the oil consumption, but still far from the no oil usage as before.
Ran my rebuilt 292 on 30W Valvoline for about 30 minutes to break in the cam. Switched it for 5-30 valvoline for 300 miles. Switched to 5-30 Mobil 1 at that point and that is what it I've used in it for three years now.
