John - from what I have read in the past, the N42 block is completely siamesed between the bores. No cutout for water passages so there is more material between cylinders. Offset boring is done to ensure even cylinder wall thickness for all cylinders.
I agree with all the arguments against the 3.1 turbo build. I really had no plans to do this build. I just wanted to see if anyone has done this successfully in the past since I do have the pistons. I think it can be done but it's just too much time, money, and effort than I want.