hmmm number 1 rule...make sure you're not chasing problems faced by
poor test equipment!

Well got rid of the scope probe and used a direct connection with some
50R coax, suddenly I can see the actual oscillator waveform (was
completely killed by all 10 sets of probes I pulled out of the box,
some are 100Mhz rated). So I now know when its oscillating or not.
Also, the 200 odd MHz reading on the frequency meter was caused by an
impedance mismatch doubling the frequency. With 50R input on the
frequency counter and a suitable output resistor on my oscillator
buffer amp I get the correct frequency.

Also I'd made a silly mistake which was throwing me (causing no low
mixer output)...I connected a 455kHz IF can filter can across the
output of the 612, but the impedance was too low, so it was just
hammering the output. With a suitable 1.5kR ceramic filter I can see
tuned carriers. (My excuse is that I was suckered into it by having
used a similar tuned can on the input of the 612 in the past!)

So...a bit of progress. Still looking out for a good HP spec with
300Hz res band option! Everytime I see a skip I look in
hopefully....

Thanks to everyone who provided their thoughts on this...its helped a
lot