Hi NK, MW and Charlie,
on a recent scrap SP motor I found, I saw the under mounted chunky type module for the first time. No wonder Victa charged extra for this new feature as it looks like more of a big deal with the chunky unit. Full of surface rust.
I replaced one that was already compact on another and took NK's advice and mounted it on top using a tiny nut and bolt instead of a pop rivet (my idea). I had to use needle nose vice grips on the tiny nut underneath as there was no other way to hold it there while I screwed in the little screw bolt.