I just skimmed through all 8 pages of this thread, OYE!
In my 240z, before the LS1 swap, I had a nicely built L28 engine with SU carbs and MSA Header and sport exhaust kit. It also popped on deceleration. Like you OP, I didn't like the sound. I added an inline resonator and the noise was much subdued but not entirely gone. Made it much more tolerable. I didn't notice much of a drop in power. But then 200hp was not enough, hence the LS1 swap.
Sorry but I don't recall which resonator I added. It was too many years ago. I did get it on eBay. I believe it was 16"-18" long.