I have run many combinations over the years. I find that it is more a matter of the kind of sound you prefer. If the pipes are larger 2 1/2 to 3", you get a very low rumble, as the diameter is reduced, the tone changes to a higher tone.
I don't have an X type crossover, I have always used a piece directly across the two pipes just back of the connection to the headers. I keep promising myself that I will make the next exhaust system with a bolt up flange between the two sides, but I can honestly state that I have never had a situation where it was important to remove only one side, so I keep putting it off.
For your application, 1 7/8' is very reasonable.
Bob
Nowadays, I prefer to use the resonator/ turbo muffler setup because it is efficient and mellow.
