It is done the same way for the KW & ZW.
It is possible to run new & old transformers together. You should phase to the new as the master transformer because they are usually in proper phase to the "big blade, on the plug. Always choose one transformer as master to phase to with trhee or more..I forget why 
. Something odd and not likely using/ crossing the accessory taps.
I use voltage measuments or bulbs(18-24v or you might cook it). Sparks are guess work ime; I've crossed them before doing it.... bright street lights 
Mixing other transformers may require more thought and limit tap functions because the variable posts letters/taps change, but those two are easy; U to U then check voltage across the throttle posts at even throttle positions. Do the test of choice, and flip an ac plug if you have to.
