Its a bit of a mystery! Since my engine in the starion is smooth till you let off without any noticeable vibration at any rpm, but other engines Ive had........... was terrible!

About the broken Power steering pump brackets, almost all of them get a crack, I have like 5 of them (was recently looking for them) and pretty much all are cracked but only one would be unusable, some of them was with bs and some without, basically I think not so good design.

That said the theory behind it is sound, but you must do the maintenance to back it up! Replace the bearings when you do the chain, adjust the chain a few times between replacing the chain, and need to make sure your oil pump is 100%.
And fact is some 2.6's run alot more vibration free then others for no apparent reason.