[Geek44]

Have built them both over the years. I doubt they are still available...at least I haven't seen them. Funnily, a guy brought the P-51 kit to my club meeting this month and it looked as old as it is.
From memory, the Harrier is an excellent kit that features moveable jet nozzles, removeable panels to show off the engine and a pretty good cockpit. The P-51 is also pretty good but the shape of the model is a little bit inaccurate, but that wouldn't bother most people...it's a bit short lengthwise I think making it look 'fat'. It's still a very good kit with lots of interior details...from memory, the two versions offered are a blue-nosed machine who's name I forget (I was looking at the box art two weeks ago...hello alzheimers) and a red-nosed 'Ridge Runner' with a wild pig motif. The biggest issue I can see here is all that expanse of natural metal. Highly challenging.
The other thing to consider is that if indeed they are unavailable, they're collector's items by now and probably worth some bikkies if they're complete in the boxes. I know Airfix have re-released some of the 1/24 range (FW 190 for sure) but with different box art. The originals (I'm very envious) are classics. I built these as a kid mate...you should go fine.