How are Lario cam followers different from other Small Block tappets ?

[unclepete]

Is the bore in the block different , or the pocket for the pushrod , or could it be as simple as the foot diameter needs to be smaller to avoid making contact with neighboring cam lobes ? Lario tappets are expensive , and I'm looking at a almost new set from a V7 750 for $40 . Would be simple to reduce that one diameter .