Believe he has a Spirit 750DC, at least that's what he said and his profile pic is a white spirit, so pretty likely a 750DC so good news it's chain drive but honestly it's not much easier if easier at all to fit a 300 tire to the chain drive, you'll have to figure out how to offset the chain to be further outside and there isn't much room at all plus you need to widen the stock swingarm, figure out how you're going to run rear brakes(a drum won't work with a 300 tire without a TON of work) swap out the rear wheel, make new axle spacers, figure out your fender...
Just don't do it, so much work to make your bike handle worse. You don't at all need a 300 tire on the back, you don't even need a 240 tire, just looks meatier and handles worse IMO. VTX rim re-lace and a 200 tire on the 4.5" rim is all I would ever do, I never need anything more than the 170 I have on the back now so someone wanting to nearly double that to 300 just makes me wonder...