Here is another statement from their Chrysler tech notes:
"Even though COMP Cams® roller lifters will work without oil system or lifter bore modifications, it is highly recommended that on any racing engine the lifter bores be modified. This will ensure that in the case of a pushrod failure and the lifter coming out of the bore, adequate oil pressure will be maintained. The proper procedure for this modification can be found in any of the materials available directly from Chrysler, or any top engine builder can perform this modification."