u joint question

:read2:on my 68 valiant i have the 225 /6 and 7 1/4 rear..i want to replace the u joints,the parts stores want to know 2 things..bearing cup size,do i have 1.078inch or 1.126inch??yoke size,is mine 2 1/8inch or 2 5/8inch??i would be greatful for any help..