I finally got some time to finish up, and today I started the engine with the new "preload" settings of 3/4 turn off from bottoming out. It's very noisy, obviously coming from the valve train, but not alarmingly so.
I let it idle to full temperature and the electric fan cycling on. I blipped the throttle a few times and held it at 1500 rpm for about 1/2 minute. No decrease in noise.
I'm sure I can increase the preload to 1.5 turns and turn these effectively into solid roller lifters but that defeats the purpose of having quiet, low maintenance hydraulic lifters.
I guess from here I have no choice but to pull it all apart again. What a chore. I wish there was some way to diagnose this with just the valve covers off.
Once I get it apart I'll check each lifter bore for oiling. I can't believe he'd screw that up by plugging most of the (at least 12 out of 16) holes. I don't see how it's possible, really. I'll have a conversation with him before I do this.
I'm thinking maybe that the taller roller lifters don't have the oiling area in the right place for this engine. Maybe the oiling holes are "trapped" in the wide OD portion of the lifter. If that's the case then the easiest thing to do would be to machine a wide, shallow groove in each lifter to intercept the hole and pressurize the narrow OD area.