This would have made a great station wagon.  However, I took the easy way out and built a pair of these, one to match the box art, which according to research was the only correct colour for the factory 421SD.  This was detailed under the hood and I used a circle template and a white gel-pen to make the skinny whitewalls. 

I also took on an enjoyable assembly and gel-pen detail project while on the road – the mint green custom kit, every piece lovingly separated from the sprue, cleaned up, painted and packaged individually, then shipped from China for only $4.  Yes, a ProShop version.