Ideas on what's causing my click/tick/rattle noise?

I would take a close look at the rings/ring lands. If it was detonating that bad, you might have a problem there. I have lost a couple of piston/rings, from detonation, but the rods bearing were still fine.

Agreed, this is on today's agenda when I get done with work.

One other thing I would check is the bearing clearance. Is the crank std size, or has it been turned? If the crank has been turned (some time in the past, such as .010 under) and standard size bearings were used, it would lead to excessive clearance. Have the crank micked, and look at the back of the bearings. They should be marked as to what size they are. It is rare but I have seen the incorrect size bearings in a box. I always double check with plastic gauge.
(the ideal way is to install the bearing in the rods, and measure with a dial bore gauge, or inside mic, and compare to the crank journal measurement, to determine the oil clearance)

I did check the clearance when I originally assembled the motor. It was bored .030 over and cleaned up at that time. All the rod and main bearings were in spec using plastic gauge.

This week I had the crank and rods checked after I found the bad rod bearing, they are all OK and ready to go back in the block. I have a set of new rod bearings, but I think I'm going to install new main bearings and rings to be on the safe side. The mains look good and I will have a report card on the rings later today.