Are they popping like an oversized oil can? (the kind that pop when you squeeze the bottom) Or is it more like a soft backfire?
If the first is true there could be a loose baffle. The old turbo muflers were bad about that. More than likely, you are just getting the typical unspent fuel pops while the engine is winding down. Something that the crossover will not eliminate.
In your case though, an H pipe would make the sound much nicer. I just done Dynomax 88022 long tubes, 2.5" duals with balance pipe and Flowmaster 40's on my 72.
It has never sounded better!
