340 rocker set up???

Right, once more...
You need to "buy pushrods for adjustable rocker arms", the length would depend on what changes from stock have been if any. Otherwise, using the appropriate OE length
rods, hyd. or mech. will do. Edit time.............
The rule of thumb on them is the right length pushrod will only have the adjuster showing 1-2 threads out of the bottom of the rocker arm, & it's not a bad one. There are
lots of things to check & perfect geometry-wise if You want to go there, but for what You're running, You should be fine.