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I reached out to LAsrkspur/Monster ModelWorks and they provided me with a solutions:
A) Although somehow I had overlooked it on their website, they provide corner pieces that match the sheet https://www.larkspurlaserart.com/product-page/ho-scale-1-8-aged-american-brick-corners Problem 1 solved
B) For the cornice issues, they now offer – just went up on their web site yesterday in fact, perfectly matching 1/32 in thick brick sheet that can be used to model layered cornices at the top of the wall.
C) They also pointed me to an MRH article that is an incredibly detailed 29 page how to entitled, “Scratchbuilding With Monster Model Works Brick” by Dave Karkoski that provides tons of details and tips including how he layered the cornicework.
Jimmy at MMW was incredibly helpful and fast to respond to my initial query in the “chat” box on the Larkspur website https://www.larkspurlaserart.com/
I recommend them highly!
Best,
Ed