Just did mine, 1" shaft. 1"x 1-1/2"x 4", Duramax part # is BETTY sourced at bargainboatparts.com for $38.30 thay also had my GFO packing 2' of 1/4" was less than $7.00.
Neal
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.