Well, would you believe, the thing actually works!!
In view of the FET and the questionable pin out, I had very low expectations that it would oscillate. However, I connected the battery and scoped the base of the BC109 driver transistor and low and behold there was a thumping great sine wave of about 1Mhz!!
Injecting a 1Khz tone (found on the internet: where else!) to the 0.68mfd input capacitor, produced a nice AM envelope as shown.
I adjusted L2 for maximum amplitude and then dug out a valve radio to try it out on.
I had not listened to a medium wave radio for at least 10 years and had forgotten just how bad it sounded (no, don't throw things at me!). Hearing music limited to 4.5 Khz came as a bit of a shock! I remember, years ago, when radio 1 was on MW, Steve Wright described it as "muddy radio"! I always looked forward to the times when it was allowed to use radio 2's FM transmitter.
Once my ears had got used to that MW sound again, and with the right type of music, it actually sounds pretty good. I'm sure a better radio would help as well: this Defiant is pretty crappy!
So, all in all, my conclusion is that this is a great little design which is easy to build. I probably spent about 2 hours in total building it and asking the questions about the FET's pin out and the coil connections. My construction was probably more crammed than was necessary, measuring only 2.25" by 1.5". I'm very glad it worked first time as removing components would have been a real pain. I think the 'perf' board was actually more convenient than Vero board as you don't have to worry about breaking tracks.
So thanks Ian for designing such a handy modulator: I will be building several more I think!
All the best
Nick