When referring to a out drive, what is a mounting stud ?

Stud for mounting the drive to the bell housing would be my quess. Ya got 6 of them.
http://www.perfprotech.com/store/ass....aspx#assembly

Part #2 in the diagram.

Yea thats what i originally thought also. But on the price sheet it says Mounting stud $4300.00 they might be referring to the whole upper drive. I'll figure it out thanks for your help. I appreciate it.

Any double threaded fastener, one threaded end stays in the mating part and you usually have loctite hold it in. The other end has threads also that you put the nut on to hold the two parts together.
Studs are great for assembly because you don't have to "find the threaded hole".

Studs are also superior in achieving a predictable preload, as you don't have to overcome tons of extra friction of turning a whole bolt. Also, it's better for aluminum not to move the bolt threads under load; let the nut/stud interface do that.