First Engine Build

The rocker angle depends on both the pushrod length AND the installed valve stem height. If the valve stems are the right height to get the rocker angle right with valves closed, then the right length of the pushrods is all that is needed. The adjustment on the rockers makes it a littler easier to take up an variations. If the valves are not the right height to get the closed-valve rocker angles right, then the valves are either 'tipped' (ground down) if too long or replaced if too short. Hopefully, your shop got the valve heights right for the rocker angles when they set valve height, but I would double check each valve to be sure.

If vavles too long, then that is where some folks try a set of shims under the rocker shafts. Any shims need to be steel, not AL or brass, as the AL and brass will mushroom out with heat cycling and the rocker shaft will get loose. (A hard alloy like berylium copper or a hard AL might survive but why bother.....) I would prefer to tip long valves; shims have several possible issues.

BTW, I just read this thread, and I think you made a good decision on the flat tappet vs roller. You're cam is not that wild, and you are not after each little bit of lift and duration, so as to demand the rollers. Flat tappets have run great for decades.

And if I can add an IMO, break in the engine on regular non-synthetic oils and then switch to full synthetic after a few thousand miles. You will be happy. Mobil 1 at Walmart is not all that pricey.