It will depend a lot on what you are going to do with the pump. Inside show piece that does not get a lot of climate change or Outdoors in a variety of sun and weather.

For strictly a show piece, I would use a basecoat/clear coat. Powder coat will not adhere to any type of body filler that I know of. If your tins are clean metal then I would use powder coat if the pump is gong to be displayed out doors.

Just my two cents here.

Hope this helps,
Tom

Owner of Classic gauge and Cluster. www.classicgaugeandcluster.com