I don't know about when you hit the gass, but if you want it to pop when you let off the gas:
Choose too large of an exhaust pipe that will eliminate good scavenging at low rpm. I'd suggest a 3" pipe for a 235 single exhaust. Get too large a muffler, the flowmasters do sound good, but get one that is sized too large for your engine (get one sized for a big block). Run a single all the way.
I had this on a 4.3L V6. Had a real quiet tone at no load and moderate rpm. Put a load on it and it opened up some (typical flowmaster rubmble). Get off the accelerator quickly and you got that pop pop pop you are talking about.
That should do it. It won't help your performance at low rpm, but will help some at high rpm. Had I wanted to spend the money to redo this exhaust, I would have done it all with 2.5" pipe and a smaller muffler for better low end torque.
