i have never spent any time confirming this idea but a friend of mine that owns a machine shop told me that by looking at the cam bore bosses you can get an idea of how much core shift the block has. i don't know how reliable this method is but it's certainly worth mentioning.

look at the cam bore bosses at both ends of the block if the bored hole is noticeably offset in relation to the boss then the block has a lot of core shift. of course having the block UTd is the best idea especially if larger overbores are desired.