A set of custom, proper length pushrods is a lot cheaper than wearing out your valveguides, which are not cheap to fix. For an even better example of what happens when valvetrain geometry isnt correctly set up, read HOT ROD this month. They blew up a 5.0 on the dyno by f'ing up the valvetrain, which wore out the exhaust valveguides, which in turn allowed a valve to tag a piston and blew up the engine. Excellent article!