Soo... Promar said that blocks are their shortage. I said I have one each of '93, '00-'04 and '06+ blocks. They said they aren't interested in bartering. I replied with a more polite form of "you sure about that?" They can still hone whatever block I provide, even with the torque plate.
They use Federal Mogul "rebuild" bearings, which are +0.25mm on the OD and -0.50mm on the ID. That is the only size those are offered in. My last experience with cutting a crank didn't go well, so I'm no wild about those. Owing to the change of shape of the main bores, I'm wondering if I need to get mine line honed with the heads on. I did that on the '93 block by skim cutting the lower crank case. The surface finish on the top of the '06 lower crank case is VERY coarse... I wonder if this has anything to do with GM's swap to RTV as the sealant of choice for the case halves, although this block still had GM's case half seals.
Anyway, since a solution wasn't forthcoming there, I bought this:
https://www.ebay.com/itm/133340495195It's what I was looking for in the first place, but it wasn't listed when I started looking... besides, seeing how the '06's worked in different ways would have been harder without taking one apart. At least that's what I'll tell myself as I pay the credit card bill.
EJC Performance is an interesting outfit... they do business with a bunch of junk yards around them, taking damaged engines that the yards can't sell as running engines, then breaking those down into major components (blocks, cranks, cylinder heads) to sell. They have stuff from a whole lot of MFGs covering US, Japanese, German and whatever else. Sometimes the engines they get have damage as light as a cracked oil pan, but the yards just don't want to mess with them. EJC also scraps damaged components (spun bearings, etc.) as their business model is to sell usable parts and not have come-backs. I found their website and called them. The guy I spoke to actually went to the block on the shelf while I was on the phone and looked at it for me. No scoring or pitting, just normal wear. Decks didn't look like it had a head gasket problem. I threw down. He said they ship Duramax blocks freight, but the Northstar block would just go UPS ground, which is also pretty wild.
I'll still go to Promar to have the bores honed, but may have it line honed locally... WITH the heads bolted on. I need to get the lower crank case decked a smidge, but prototype guy is trying to invent himself as an engine machinist, so I'll let him take that on.