I know what Mike designed his lifters for - there are more reasons to bush than oil pressure leakage. A milder engine they are a good reason not to because normally the budget is tight. But - if this engine is going to be raced, and is going to run a solid roller cam, the lifter bores should be bushed. In addition to properly controling oil pressure leakage aroudn the lifters at any position, bushing corrects factory geometry that is as good as the accuracy of the deck heights (assuming you know how bad those are) and in the event of valve train failure the bushings allow the lower end to remain intact because they don't allow the oil to flow out the lifter bore when the roller lifter kicks out. Break a rocker at 5K rpm and the lifter come out - by the time you realize the engine's missing and get the car in nuetral and the engine off - the lower end's already suffered damage from no oil. If your budget is $9K we're talking about $500 or less than 6% of the engine budget. I have the utmost respect for Mike, and Brian who also came up with drop in lifters - but I believe it's foolish and irresponsible for the builder not to spend that when the risk is that high of more damage.