I just purchased a preowned Parker 2520xl with dual Morse Controls for
each station. Each control has a both a red and a black-knobbed lever.
Is the red lever for rpm adjustments and the black lever for
forward/reverse engagement?

Traditionally, yes.

Remember red=fire=fuel :-)

However, if the boat was previously owned all bets are off. Don't assume that
anything is hooked up or installed properly on a used boat. (Sometimes new,
too).

Also, for starting the engine, can I
assume the neutral lever positions are straight up on the transmission
engage lever and then full aft for the rpm lever?

Thanks,
--Brett

Straight up for nuetral, assuming the cable is properly adjusted. If the engine
won't crank, wiggle the tranny lever a little bit.
Lots of times the cable is OOA and the lever has to be slightly forward or aft
of center to activate the neutral switch.

As for the throttle cable, it will depend a lot on whether the engines are
carbed or injected. Lots of times the carbed engines need a couple of "pumps"
from a cold start.