I know what you are saying, the key point is to be a Sandman there has to be proof, not the other way around (ie prove it isn't).
Whilst many think being a 308 and 4spd leads to the question "is it a Sandman", if it turns out not to be they think it is a "highly optioned" ute or van. Trouble is for example, for all of HQ-HZ a 308 was an option regardless of whether a ute or van was a Sandman or not. Along with the 308 came an M21. So a ute or van being a 308 and 4spd really does not tip the scales either way towards being a Sandman or not. Incidentals like U17 instruments and bucket seats were cheap options in comparison to mechanical options like V8 engines, power steer, air and especially TH400 hence lots of commercials got them if they were ordered rather than bought from stock or schedule. In fact the best pointers to a ute or van being a Sandman is the colour, relatively not too many non-Sandmans were produced in some colours especially metallics unless they were Kingswoods which rules them out most of the time from being a Sandman anyway!
The one that may always bite people in the @rse the most is a reduced GVW option (ie XU4) along with buckets and 4spd on a late HJ, HX or 1977 plated HZ, epecially on utes. These are rare but a few have come up.