Tailgate and a hood with correct emblems should do it. The rest is pure Ford.
Modelhaus currently has a '57 Mercury truck in the catalogue and the tailgate is available separately so you may be able to adapt it. As for hood letters, it would be great to see a photo etch set of both the '53-'56 and the '65-'68 letters... otherwise, we'll just have to cut them out of chrome tape
Looks like this reissue has the custom chevy fenders restored; one of the reissues I have with the blue truck on the box didn't have them.