Nice relic ! I like these - and as someone else said on the forum, they're difficult to 'fake' !
I'd suggest you have a couple of choices : leave it in relic, 'salty' condition and at a later time, add a perfect one to your collection as a comparison ( they're not too difficult to find ). Or, as you say, it should clean up quite well and you should be able to find a handset and plug without too much trouble.
The FF33 isn't considered to be very 'exciting' by many collectors, but they went everywhere the Wehrmacht fought and can be seen in use many contemporary photos.....
Thank you Martin i also like it as it is part of the field gear :P
i just want to remove some rust to prevent further corrosion