Chaps, this is dead interesting stuff. Not sure that I follow ALL what is being said, but still good nonetheless.
In the previous post I mentioned that both turrets need four servos each to operate. Apologies... I mislead. Each turret needs just THREE servos - not four. The usual 'landing gear' switch (Ch.5) is to be the switch that changes the three R/C pulses at PORTA to either PORTB.0 to B.2, or B.3 to B.5.

Using a 4MHz crystal/resonator I found the output gives a slight amount of servo jitter. Not much, but enough to be annoying. Swapping the Xtal to 10MHz does counter that unwanted jitter, but then the 'reverse' timing becomes out of sync (servo neutral shifts to somewhere other than neutral).

I like the AND gate suggestion. But in this case the three servos which are not being operated are to be set to their neutral positions while they're sleeping.

The downloadable version is PBP is limited to around thirty lines of code. I'm toying with the idea of purchasing the full-working version, but reluctant to splash out £££s if I can't even understand how to write simple code for gadgets such as this.
You guys obviously know what you're doing so I'm hanging on to your advice.

Ace': Good luck with the breadboard lash-up. And thanks!
Same goes for you too, Ski'.... Thanks for all your input with this.