Good question. I've been wanting to convert the Entex Rolls into a drophead coupe for years. The hold up has been trying to figure out how to replicate the boot.
There's a set on ebay listed as:
🌟"Dagmars" Bumper Bullets 1953 Ford F100 1:25 Scl 1000s Model Car Parts 4 Sale.
The AMT 1949 Mercury has a custom grill bar as well.
I've been using microsofts 3d Builder for things like this. I'll make the hole slightly larger than I need. If I need a 2mm hole, I'll make it 2.5mm or so. Then I'll send it through the slicer.