Well, that shortens the list of variables, but (except for parade purposes) the GMC rocker isn't up to big springs. Of course, the problem is that there isn't anything else.
Milling or shimming the stands is also a variable, but as I said you won't know until you get closer. Pushrods are the very last purchase.
Which cam does it use, stock GMC lobe positions or special?
The stock valves are:
Ex - In - In - Ex - Ex - In - In - Ex - Ex - In - In - Ex
The Fisher/Horning looks like this:
In - Ex - In - Ex - In - Ex - Ex - In - Ex - In - Ex - In
Not sure if actually made for GMC, but common 12 port layout:
In - Ex - In - Ex - In - Ex - In - Ex - In - Ex - In - Ex
These 2 last require special billet camshafts.
