[steelcomp]

Rick,
Your question has merit, but I'm not sure that there's the side loading you're thinking of. At just about any given point of travel of the valve train on a canted valve head, the push rod and lifter are off line, thereby causing some side loading. An offset lifter is usually paired with an offset rocker, so the angle really hasn't changed much, so I don't think there's "more" side loading going on. And yes, they (lifters and blocks)wear. Lifters, especially, since cast iron is more durable (harder) than steel. Look at a set of used roller lifters some time and see what they look like. It's why most guys will sell a set after a season. The sides are worn out. The reason most flat tappets dont wear like that is they never have the kinds of spring pressures that a roller sees. Also, a roller lifter dosen't spin in the bore like a flat does. I would think this would actually add more friction, causing more wear in the bore, but it's neglegable.
Blocks that are bushed are usually done so to correct mis alignment from the factory. (Does Shelby bush theirs? Most alum blocks I've dealt with aren't.) I don't think it makes a whole lot of difference, but there is some parasitic friction there to consider.

Hmmm.
KC?