I have a B3 on my '69 ES330 which works well but required a fair amount of work to get it there - I ended up grinding material off the bottom of the Bigsby to buy break angle over the saddles. If it's on the low side, you might struggle to get it to work at all.
If it's around the average, it will probably work but you might notice a lack of sustain and you might have trouble keeping the top E in its saddle if you bend strings or have a heavy picking hand. If the neck pitch is on the steep side, a B3 will probably be fine. Although by the time the Casino emerged the vibrato models either got B7s or an Epiphone branded unit, they initially went with the B3 for first couple of years of the ES330 version - it seems like they had problems getting them to consistently work with B3s hence the change to B7s. I would discount the B6 as being longer it sits fractionally higher on the body carve and believe me, you need every 1/2mm to get these playing well. Whether you can use a Bigsby B3 or B6 is pretty marginal and will depend on the neck set of the individual guitar. I vaguely remember those - made by Tereda who make the Pro Line Gretsch guitars and assembler in the US, there was a natural and a sunburst version.
