Finally got 'em and they're shipping.
And worth the wait, too.

They're set up to be vendor ship direct, which means it ships to your dealer direct from the machine shop in Auburn Hills, MI.

Vendor ship direct also means dealers can't see any warehouse inventory, so they might be a little nervous promising an arrival date. Tell them not to worry.
Order it, and it'll show up.

Anyway here is the spread of part numbers:

P5155507 4.125 finished bored, fully machined

P5153897 4.055 finish bored, fully machined

P5153898 semi finished machining, 4.114 bore, can be bored to 4.185

P5155630 semi finished machining "builder's special", no assembled components, allows user to finish machining to their unique requirements and aftermarket bearings if necessary

All blocks are made from casting P5153896. (P5153896AA is the most current and most often seen casting).

They're 98lbs lighter than stock. They're nice to work with, and are quite a departure from the old iron I am more accustomed to.

Here's a couple shots of an aluminum 440CI engine.