I'm anal about the bearings too. Dry back so sets down solid in the bore. I handle them carefully too. Get a hard spec of dust trapped on backside of that bearing a couple of times and you'll reconsider. They often come out of the box utterly filthy and static makes the detritus on them tend to stick. On install they need to truly be surgically clean.
I wanna hear about why you can't run the engine at 2500. I've done it on hundreds of engines, including 700+ inch race motors costing $50K each.
Add to that every cam manufacturer on the planet will disavow cam warranty as soon as you tell him you idled it for any length of time beyond a few seconds. You want FULL oil pressure/splash on the cam lobes RIGHT NOW, they wear more in the first 10 minutes than they ever will after.
You NEVER longterm idle a brand new motor with new cams until past initial break-in. A few seconds,say when you first crank it, to listen for abnormal noise is OK. I lightly rack the motor a time or two. Lots of times I'll do the initial start with no water in motor, I like to 'cook' the head gasket a bit and ring/wall temp comes up faster to bed in quick. Shutoff and look for leaks. Wait maybe 10-15 minutes and add water. If all well then next crank it goes to 2500, it doesn't have to be exact. You're looking for higher oil pressure. Somebody stands over motor with trickling water hose to hit radiator if necessary, you want motor to get hot but not too hot.
Doesn't have to be strictly 20 minutes either but need at least 10. We probably did the pro stock engines shorter simply to save ring and valve job wear, rather do that on the racetrack. There's no reason at all but good result to stretch time on a lowly stock motor though.
Maybe it's a boost thing, if so I'd be looking to kill boost during break-in.
To OP, ANY motor that's been disassembled needs a bit of time to realize it's back together. I wouldn't long idle at first even on a dead stocker. Get it out and drive it quick so varied engine speeds can help you. You need to at least observe new ring break-in procedure if I read the posts right.