Think about it this way...everything around the t-belt is worn after 138K. That means the cam gears etc. So the most pliable or flexible item is the rubber belt. To break in other new metal/hard items carries an inherent risk of inbalance or noise in the whole chain of action. They run the risk of becoming minimally dissimilar components near term which causes extra pressure on the old items and are thus more prone to causing failure. Keep everything the same as much as possible...that's the best scenario.