Nobody knows how many. There were 118 68s built and estimated 5000 or so 1970s. 69 production numbers don't exist, but the Toronado Chapter OCA has generally accepted that 10% of 1969 production were W-Toro's.
Basically, if you have the OM transmission with a matching date code and VIN, you have a W34. It's the only positive external identification on a 69. You can't go by the presence of dual exhaust as many 375 horse 69's have had it installed, and you have to pull the engine out and apart to ID the cam.
Contact the Toronado Owner's Association
www.toronado.org . See if someone there can steer you to an appraiser familiar with Toronados.
Up front- don't expect the W-Toronado to fund your kid's college or your retirement. Except for the 66, the cars are way under the hot collectible radar, and the 68-9 front end styling is an acquired taste.
And yes, I own a 1969 W34 myself.