383 rebuild - kinda whimpy on the dyno?

Wow. .001 doesn't leave much room for error.
One of the disadvantages of closer bearing clearances is that it can raise both bearing and oil temperatures. That’s no problem as long as the bearings and oil can handle the heat, but if they can’t it increases the risk of lubrication breakdown and bearing failure. The tighter the clearance, the more critical perfect machining has to be. Perfectly round, straight and smooth journals. That’s why high quality synthetic motor oil is the norm if you are building an engine with tighter than normal clearances. Don't be afraid to use an oil that starts with a zero.