Hi arch2b,
I don't know exactly the meaning of "negative/positive shift" by using in rc-controler.
But maybee it is only the rule to transmit the forward speed in a short puls of the signal and the backward speed in a long puls.
So you have no problems to use them in the same truck. Just activate the "servo-reverse" and everything will working.
Some very old controler (<20 years old ) works by a negative voltage signal. So their are not compatible to the new recivers or servos. Additional the old parts are bigger than our whole cars ;-)
best regards
Thorsten
www.mikromodell.de