A billet block is a solid block and has no water jackets and really is not a street piece - but if the block has drilled lifter oiling then yes you can bush it - otherwise its splash oiled and bushing has some advantages but if its new probably not worth it unless you are going with an exotic type lifter - if it is a lifter oiled block then bushing the lifters can be done for many reasons like push rod oiling - or the one reasons already mentioned.