Thanks so much for the reply. I was able to find the fan using the info on the existing motor, and then the Baldor website. (Sorry, the forum won't allow me to post links because my post count isn't high enough)
baldor.com/products/product.asp?1=1&product=AC+Motors&family=Definite+Purpose|vw_ACMotors_DefinitePurpose .
I think the 3450 rpm fan CNL20172 is the correct upgrade. It's .17 hp, where the existing fan is a CNL 20134 at .13 hp. I found it for $155 here:
mrosupply.com/product/26982-Baldor_Electric_Motors-Motors_AC_Motors_Definite_Purpose .
The eBay seller you bought your cyclone from has another model:
ebay.com/itm/Cyclone-Separator-for-Dust-Collector-/280840027122?pt=LH_DefaultDomain_0&hash=item41635ebbf2
I contacted him and he said he has sold many of that model specifically for coffee roasters. It has a 4" inlet and a 4" outlet so it will connect with the outlet on the Ambex and most dust collector fans with no adapters. I tried the small Harbor Freight fan he shows in the first photo but it was too loud so I went to the slightly larger one which is quieter. I may also try this fan which reviews indicate is very quiet:
amazon.com/PSI-DC660P-Horsepower-Collector-1-Micron/dp/B0000223WS/ref=pd_cp_hi_0
Our roaster is in our coffee house so we want the fan as quiet as possible. Do you feel that the 24 gauge steel that the cyclone is constructed from is strong enough to support the weight of your fan? I'd like to order a cyclone from him, but I just wanted to get some feedback from someone like you who has used one. I like how you installed your fan up high on the pipe instead of on the cyclone. Do you feel that works better and that it's quieter away from the cyclone?
Thanks,
Clint