Tck,
Popping and banging in the exhaust is usually caused by air leaks either at the cylinderhead or the pipe to silencer joint. This can be made worse if it is accompanied by a rich idling mixture. Also, the original exhaust system had the pipes going into the wafflebox by about 8" - with the last 7" slotted on the inboard side, and the ends blanked off. The original waffleboxes also had another baffle behind the large brass plug (in the centre front of the box). This was in the form of a tube (same diameter as the exhaust pipes) with slots on either side. Often (after 60+ years), all that remains is a rusty ring located in the register in the dividing wall across the box.
Regards,
Eddie.