I agree,, the 8 1/4/8 3/8 axle shafts will interchange.

My 88 was a 318 NP435 shorty.
I thought it had a 8 1/4 till I had a counter clown buddy at a dealer run the numbers.
It came out to be a factory original equiped 9 1/4.
That 9 1/4 diff that I have was going into my 87 RC till it met its demise.