Lifter bore bushings

The latest parts are designed to drop in without them. that being said - That's for cheap and easy, not for performance. I will not run any solid roller without bushing the bores.
1. It adds stability to the valvetrain because as OMM said - it fixes machining issues with the factory bores.
2. It adds safety should you have a failure and a lifter pop out of the bore because unless it happens at idle by the time you notice it and shut the engine down and it stops turning - the lower end has starved for oil (seen this twice personally).
3. It adds control to the problem of oil pressure bleeding past worn lifter bores which means you can set up a better oil delivery to the top end and lower end.
4. Because of item 1. it lengthens the life span of the roller lifters.
5. Becasue of item 1. it gives you "free" horsepower by removing loss of valve control due to harmonics and truing-up the roller to lobe relationship.

The main reason I do it is 2. But all of those are true over no bushings.