I have the old Airfix kit of the Westland Sea King Air Sea Rescue helicopter, which I believe is an HAR3 version. I would like to present this as a US Navy machine, but am not sure whether any modifications would be required. Obviously, a different paint scheme and markings will be needed, but I am wondering whether the window arrangement down each side of the fuselage would also need to be changed ... also, any other details that would only be appropriate for the RAF version.

I seem to be answering my own question here ... it would appear that none of the US Sea Kings have the bubble windows towards the rear of the fuselage. I have also found no images of them equipped with the large radome (on top of the fuselage), and they appear to have five-blade tail rotors, as opposed to six on the HAR3.

I have been out of the country working.

You are correct on the differences. Also, depending on which version of the kit you bought,do not use the square air/particle separator, nose radome, or SKUA missile mounts.

There can also be an issue with the tear drop bulge on the trasmission housing near the rotor. Sikorsky (USN) birds do not have that, Westland (Bristish) birds do.

HTH