Pinion Seal Replacement

Have a 741 case, 1-3/8" pinion.

Did some research, and found some information that says the seals for 1-3/8" and 1-7/8" pinions are the same, even though some part numbers say they're different.

http://board.moparts.org/ubbthreads/showflat.php?Number=4854206

[ame]http://www.wichitamopar.com/wp-content/uploads/2012/10/MOPAR-REAR-DIFFERENTIAL-INFORMATION.pdf[/ame]

The second link lists the national part number 8515N. I had my buddy cross reference that number and order me a seal. I got an SKF# 18708 (same C/R# is listed for 1-3/8 and 1-7/8".

After measuring the I.D. of the seal, it seems way too large to me. Measured out to be approx. 1-7/8" diameter. Isn't this too large for a 1-3/8" pinion? Does anyone know the I.D. of a 1-3/8" pinion seal?

Don't want to take the yoke off and pop the seal out just to find I have the wrong seal, especially since all the part stores around here would have to order a seal in and I'd be waiting with the car on jack stands.

Thanks