Thanks TD4438 I initially painted the shell with Humbrol rattle can Crimson. My youngest son (42) told that it looked too dark for the period look I tried to get. He said that I needed metalic or metalflake colour / finish to sharpen it up.
I went to our local Hobbycraft (12 miles) as they advertise various metalflake finishes for greetings cards! I found both coloured and chrome in plastic pump bottles. I also found again coloured and chrome metalflake in my favourite rattle can paint that I always use...Plasti-Kote. I bought coloured and chrome in the card finishes and a chrome only finish from Plasti-Kote.
I tried them all on an old 356 shell and went for the Plasti-Kote. After two light coats I had the finish I needed and so after three or four days to dry added Plasti-Kote clear gloss. Everybody I've shown it to is impressed including my youngest son!
Be aware that you are spraying metal flakes onto a painted surface which makes it very rough and to a certain extent sharp! That's why I coated twice with a gloss clear.