TRANSK - - 62 - 64 Hawk -  Small Parts kit-63 Vette T_10 trans kit SP10-50 B. Warner

T-10, four speed rear seal is  NAPA NOS15041 (old CR15041).  This is for a 27 spline output shaft.

 Seal - Precision FM9613S (aug 2007)

See this page
http://tbtrans.com/t10_transmission.htm

It also lists the tail extension bushing number, should you need one.

See:

http://www.studebaker-info.org/tech/cr15041.html