I'd be surprised if the 8, 9, and 10 speed ones would fit on your wheel with your current axle length/spacing. I know that some people had some problems with the DNP 7 speed freewheels with regards to quality and precision of the teeth while others did not. Sounds like the quality was rather variable. That might have been what your lbs mechanic was referring to.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"