SailorVee - the Mk3A Sea King (of which we have 6) has the SN500 fitted and can only engage overfly from 749' and below - probably the same as yours. I have been campaigning to get the Mk 3 fleet upgraded to the same (relatively modern) standard - your comments are true of the Mk 3, it is a steam driven heap of **** by comparison - but no-one will listen because it costs money.
You still have to get to a point (IMC) where you can engage trans down or overfly (I suspect that like ours, the overfly still means you have to fly the height manually down to 200' before it starts the TD element or you will miss the target) so you still need to be able to clear the area you are turning into (especially as for overfly the SN500 calculates it's own wind and may turn left or right from the overhead). Hence the need for a 360 radar and hence my question how you are allowed to fly below MSA IMC without specific CAA exemption?