Read the rpm/tuning chart published by Krumscheid .
this chart provides recommended length of header to band on pipe for the tuned pipes -which you mentioned .
We found that these recommendations are quite good -as expected.
DA recommends the larger cans on their engines . example a 70 -on a 50
On the Amelung site (Germany) they make the same observation on their ZDZ50 -as it is ported for tuned cans .On engines with similar porting to DA -the tuned pipes recommended by Krumscheid - should work but their maybe a small change in smooth operation.
It was interesting -checking a 160 cc twin - using the Krumscheid chart for overall lengths on the 80 cc 10/80 pipes.
going 2" longer -OR shorter - changed power to lower power.
also shorter made midrange poor.
longer just dropped power
in the correct setting (to chart) -the throttle was perfectly smooth and aggressive in response and power was maximized.