Meaning if someone already had the tool head included from the factory could they build a dual head using the parts they already have and purchase the difference individually?
Yes, Kind of. The stepper motor is a half height variant, the stock ones are too long. Replacing those is inexpensive though, and I think the lulzbot store even sells them. The tricky part is sourcing the dual extruder metal frame. I got one of the few that came through itworks3d.com , but they are very hard to find otherwise.
Also is there such a thing as a dual head extruder that can do Rigid and Flexy out of both heads(not like flexydually where one head is for rigid and one is for flex)
Not in a stock configuration. There are alternative extruder bodies that include more plastic around the hobbed bolt that will work better for flexible fillaments.
There are various DIY options, some of which can also be purchased. For example, my extruder body remix has that build up area, but since it has the overhead support structure, it’s not really suitable for use as a dual extruder. http://www.thingiverse.com/thing:1355145
You can also fit something like an E3D Titan extruder to a Taz that will theoretically output Flexible fillament, though fitting it to a dual carriage might be a challenge.
There is also an insert piece you can print and install in existing extruders to attempt better contact. I’ve not personally used that one though.