Problem solved !
I've had a closer look at the spare 'paddle' blade props in the Tamiya kits, and thankfully they're somewhat inaccurate, being rather narrow in chord for the 'paddle' type blades, and with the same, or very similar, deeper root chord and shape to the DH 'needle blade' props also supplied.
When compared to the Airfix 'paddle' blades, the shape difference, particularly at the root, is immediately apparent, and there's a good 1+ mm difference in chord width at the mid point - around 2 or more scale inches !
As the Tamiya 'paddle' blades are not far off the shape of the 'needle blades', it should be a fairly simple job to re-profile these to create a set of 'needle blade' props.
The Airfix prop spinner back-plates will need to be modified slightly to accept the Tamiya props, which again is a simple job, but other than that, the spinners and back plates fit the props without a problem.
The pic below shows the Tamiya 'paddle' blade prop, with an Airfix blade alongside.
Thanks for responding chaps, but I'm now sorted - Mosquito PR.IX coming next !