There are guys running R3/W9 setup that are hardly cutting corners when it comes to money. They use the Chevy lifters, in some cases, to move the lifter bores themselves closer which gives 'max' pushrod clearance and the most port room. There are also more choices for Chevy lifters, too. They're probably doing it for other reasons, too, that they're not sharing. The point is...the .904 lifter is nice but hardly a must.