Well, since most violins made in the last century or two have been patterned on Strads (including a rather lovely graphite fiddle with an unfortunate marketing problem), it's not entirely surprising that a well-made modern instrument might be mistaken for one. Anyone participating in such a test who can't pick the del Gesú out of the pile ought to visit an audiologist immediately. The character of the Guarneri is as different from a Strad as, say, Ethel Merman is from Maria Callas, and the Guarneri is Merman -- a lot of odd-order harmonics give it a harshness, but damn, you can hear it from a mile away. The Stradivarii are sweeter and rounder, with a much larger proportion of even-order harmonics, but with enough harmonic content to maintain that little bit of stridency that allows it to be played over top of an orchestra.

Yes, there has been a lot of research around the acoustic properties of the Cremona fiddles. A LOT. You could fill a dozen or so mid-sized container ships with zipped fiddle papers on high-capacity Micro SD cards. Not surprisingly, sounding like a Strad involves mimicking the mechanics and internal acoustics of a Strad.

A competent luthier uses dimension only as a guide to rough the shape; final shaping of the back and deck are done by ear. Tap, scrape, tap, scrape until the violin back as a percussion instrument sounds right. And that "right" sound is usually derived from a Strad or a "gold" copy of an unfinished Strad kept in the shop for exactly that purpose.

The graphite instrument, being made from a material much more consistent, controllable and predictable than natural wood, was patterned using vibrational mode analysis across the entire spectrum of the violin's range. With a stable, predictable material, tooling can reproduce the successful prototype nearly perfectly every time, and a quick trip through a sweep genny for Doppler analysis is all the QA you need. If an instrument's components react acoustically the same way a Strad's do, and those components are assembled the same way as the Strad, then the instrument should sound pretty much the same as a Strad. (The best acoustic research available concerning Stradivarii was done in the production of this graphite fiddle.)

Yes, there is a lot of voodoo mumbo-jumbo talk about the magic of the Cremona fiddles. Yes, the wood was different, the spruce being older-growth, harder and with higher mineral content on average than most of what was available elsewhere -- but there was probably more variation from slab to slab of the available spruce and maple than there would have been between the "average' log in Cremona and the "average" log in, say, Paris. Yes, the varnish was different, being part red shellac, presumably in order to give the wood a redder colour than tree resin alone would have. Both of those differences can and MUST be worked around every time the luthier puts gouge and plane to wood. What makes a Strad a Strad is its vibrational modes in minutia.

Violins produced before the Cremona variants were ukuleles in comparison. The Cremonese were rather protective of their intellectual property, and had no trouble disseminating faulty intelligence and making a big fuss about keeping things like varnish and glue recipes top secret. Misdirection is a very effective security technique. What they did differently was to try to understand how the instrument really made its music, and then to treat the acoustic (as opposed to merely structural) components as instruments in their own right. Luthiers outside of the Cremona circle were more than willing to believe that there was magic in them there beetle shells -- it's a lot easier to swallow the idea of alchemical tricksies than to accept that someone else is taking more care than you are at every step in the process.

Make a fiddle that vibrates the same way, make a fiddle back that plays the same marimba music when rapped in the same way as a Strad back, and it will sound the same as the Strad. Make a fiddle that vibrates like a del Gesú, and it won't sound much like a Strad at all -- but it will sound remarkably like a del Gesú. (Oh, and set the bridge or soundpost wrong on either and you get something that sounds like it's perhaps twenty dollars at Wall*Mart.)