Well, all MLW roadswitshers after the ZWT was put into use, anyhow.
It is true that MLW went directly from the Type B to the ZWT and, at least for "domestic" units, never built a unit with Hi-Ads (same goes for 6 motor units going diretcly from Trimounts to the short-wheelbase MLW design and foregoing the Alco-design Hi-ad).
I was just wondering how Hi-Ads got into the discussion. Since I've never seen evidence of R-S ever having Hi-ads under them (or anything else, for that matter) I was looking to clarify if this was confusion re: truck terminology or if in fact one or both R-S M420Trs ever actually had Hi-ads. They were definitely built with ZWTs, and I would say with 99% confidence R-S never had Hi-Ads under them, but I don't know what might have ended up under them after they left the R-S.