It seems that although I managed to build Andy G4JNT's PIC circuit properly, and his code is just fine, that the decoder will not yet work because the GPS module is configured incorrectly.
So now I have to configure it, which means getting it connected to the PC to run Ublox U-Center software to allow me to change the set-up. This it looks like I have to do in RS232. So, its back out with the iron and the 9-day D-types!
Update - well, it turns out my GPS module uses TTL levels, not RS232 - it even says so on the module!
My one and only USB to TTL conversion module I cannot find, so thats yet another item on order from the Far East, and yet another project or experiment put on hold for up to a month waiting.
And, it also means ive finally succumbed to the temptation to order the Airband receiver kit! Looking at the circuit for this, its clear that its a blatant copy of the Ramsey Electronics kit, but at a fraction of the price.