I put that 7 1/4 rear into my 66 Valiant, after we put a 8 3/4 in the Cuda. The 7 1/4 finally gave up the sure grip clutches last May at Mason-Dixon slant six race.
I had been running that same 7 1/4 rear (3.91 SG) since 1974 (5 different cars). Never hurt anything except the SG clutches. This is the second time for the clutches. I will install new clutches (on the shelf), and use it again.