Last night I made several styrene panels to "marry-up" the lower hull to the upper body.
I also made a lower "chin" for the radiator. I also added one of the nuclear symbols to the insert grill (I'll be taking the insert out when I paint the radiator shell its final color).
The chin section was made from a piece of Bristol Board. Bristol board is an acid-free type of artist paper which is like poster board, only thicker. To make the chin, I used an old brass door bumper. Its base (the square part which bolts to the floor, was about the width of the radiator. The top of the door bumper is curved like a half-dome (the rubber bumper for the door to hit against sitting underneath).
I cut a strip of Bristol Board one inch wider than I thought I would need and ran some tap water over it; making sure it was thoroughly soaked. I waited a minute or two for the board to soften, then I molded it over the metal top of the door bumper, squeezing and and slowly making it conform to the complex curves of the half-dome. Then I turned my wife's hair dryer on "low," set the hair dryer on its side on the table and held the Bristtol board and door stop in front of it until the paper dried. You have to hold the paper in place against the metal doorstop or it will straighten out as it dries.
Once it was dry enough to hold its shape, I coated it with a heavy super glue gel to give it strength and so the I could sand surface and remove some of the wrinkles. It's a good idea to prime it before sanding it. Bristol Board is usually white, and if you use a gray primer, you can see when you've sanded off the "high" spots.
After that, you just glue it onto the part, and prime it again. Then you're ready to hit it with the finsh coat of paint.