there's a lot of circle track racers out there that most likely have sleeves in 400 blocks. we used to run wissota mods and used to sleeve the blocks as long as bore only got hurt when the occasional BOOM! happened. this is alot cheaper than buying a new block. these and alot of other classes and santioning bodys have claimer rules. so you don't want to put thousands of dollars in a engine that can be claimed for a lot less than it costs to build them.