Corny kegs must vary in size because mine are slightly different from brand to brand and they sure are not 8.125" .. Double check the real sizes of the kegs you are going to buy. The top rubber handles might measure 8.125" but the actual stainless cylinders are larger.
Ball lock kegs are about 8.5" - 9" wide, and 25" high. With the MFL (Gas / Liquid) couplers connected, does this increase the height at all? I'm building a collar for my keezer, and an 8" collar gets me exactly 25" on top of my compressor hump. If the MFL connectors increase keg height even by 1/4", I'll have to go with a 10" collar.
Tried to find a good "profile" view of a ball lock keg with the MFL couplers connected, no luck.