For the Mitsu, since I have/had the whole clutch housing off the trans, I used the throwout guide tube to find crank center and sanity checked it with verniers on the 6G72 block, as well as with the bell pattern, since the main holes are verticaly symetric. Everything checked out to within a thou, so it's all good there. My actual allignment to constrain everything while probing was based on a construction line between the top 2 housing holes.

For the benz, I used the circular machined groove in the plate since it's concentric with the crank. I also double checked with the engine block.