I'm not sure if there is any way to check online or not so sorry I can't be of more help with that. I will though say that for such a short flight an old or new interior wouldn't make all that much of a difference to me. The old seats are comfortable enough for the less than 2-hour flight and any difference in IFE also wouldn't really matter. Unless you just want to experience a refurbished 777-300 I'd say just book whichever class you want based on other factors.

If you really want to know what aircraft it is why not just call TG and ask them?