AFAIK Teac never made any 1/2" 2-track machines, so the biggest single problem is that there are no compatible heads for it. What you would probably have to do is ask JRF or another magnetics company to adapt some Flux Magnetics (or other brand) heads so that they can be fitted to the Tascam headblock. This probably wouldn't be too hard for them to do, but just buying the heads is probably going to cost more that the recorder is worth.
I would make a point of asking JRF about it.. they sell a lot of 1/2" conversion kits, so it's possible someone may have asked them about this already.