Probably, the rocker arm geometry because there is not alot you can change easy. Not sure how many people use the lifter burnishing ball through the lifter bores? I think it is a good idea if running a flat tappet cam.
Some more common stuff, is mostly valve train related. Not checking valve spring pressures and coil bind when changing cams. Not measuring for correct length pushrods. Not degreeing the cam. Not using sealer or loctite on bolts that need it. Not pre-fitting the intake manifold and trying to make it fit when it needs to be milled. Not checking bolts for correct length, either too short where only a few threads grab, or too long where the bolt bottoms out. This is normally the issue with changing to a HV oil pump on a big block, the aftermarket bolts will bottom out right as the pump starts to tighten down. Also, on the big block oil pump, making sure the "O" ring that goes around the housing shaft is installed and lubed. Missing the "O" ring or tearing it on install can allow the pump to suck air.
When I freshed up the 500" stroker, I forgot the oil galley plug behind the cam gear. Good thing I tried to pre-oil the engine while it was still on the stand.
Distractions are a real issue when putting an engine together.
On my old 360, I was installing the pistons, and I got interrupted and had to do something for maybe 5-minutes. Went back and started installing the next piston, and I forgot the rotate the crank first, and ended up nicking a crank journal with the rod bolt.