I ordered my gaskets from Obsolete Chevy Parts
They are 2 different gaskets. The thin one goes between the diff. and the housing and the thick one goes under the cover.
I haven't filled mine yet so someone else will have to tell you the fluid capacity.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.