I have an 84 vt700 and believe the exhaust is the same setup. I ended up cutting the exhaust at the beginning of the trumpet. So cut it right before the crossover muffler.
If you look at the exhaust you will see it has the two header pipes coming off the engine then there is the crossover right in front of the rear wheel where the two pipes connect and then continue on.
You have a few options: one you could get a set of after market pipes I have seen a couple options for this. For this you will need to rejet
You could chop the exhaust and run two pipes, but you will want to rejet or otherwise have that crackle when you let off the throttle.
Or you could try to do a whole saw mod, but you may want to look into this on this setup due to the cross over being the muffler, but should make it a bit louder.
Any questions feel free to ask or pm me.