c.
Mine made so much noise up to 74 mph then it was quite,,I knew it was coming out for inspection, because, (of the V8),,,, that was the agreement when I got the wavetrac. anyway i had 10,000 miles,18 months, 127 runs in the 1/4 mile and 9899 miles of ******* the car,,( Note to Rudy) no failures during that time,on any part of the car.thank you Rudy for a great job. any way after all this ,i removed the diff. sent it to Devin, for complete tear down and inspection,, the wave trac was in great condition, but completely refurbished anyway,, the carrier bearing were fair but would only lastvery long if driven the same as before .Devin also found every tooth in the pinion cracked, the ring was ok,,, i sent a new set of gears to be installed, now with new gears and bearings, a newly overhauled wave trac, I have a brand new 307 rear for my car.
now to answer your other guestion," why do i need/want a spare 307 diff?',,will I need another R & P , don't know, but would like a few spares.
yes the 327 in in the car now with a new wavetrac,, a new tcu ,because the one I got from Eurocharge DID NOT WORK,. the one I have now works. thanks Rudy again.

the rear noise: I think because we are changing the carrier we need to double check the backlash, and the tooth pattern which was done on all of my wavetrac's,,the snap ring is the shim,,they come in different thickness ,this is how you set your tooth pattern,, with all the rear ends i broke with the 3.2 V6 ,I had plenty, plus I had to take .004 of of one to get it right. so far no noise.
Having some more work done but will be back on the road soon,, KC, and a ic cooler tank, exhaust, adjustable rear links all of them. springs front and rear,, weight balance. to name just a few things. JIM