Mancini Racing has them for $39.95 part #mopp5007709. I just installed one on my 416. It did not make a difference on how hard or easy the motor turns over. My motor is not back together yet so can't comment on the wear pattern. If you do use one I would degree your cam again with the tensioner on just to see the difference. I tore my motor down with only 800 miles on it because of a vibration. So it gave me a chance to check everything out. I'm using a good quality timing chain and it appeared to have stretched quite a bit, so I'm trying the tensioner. I'm using a gear drive timing set on my 410 so time will tell which one out lasts the other.
I think if you use a good quality oil, regular oil changes, and a good screen on the pick-up tube everything should be fine.
