See pics for how the surface prep and priming turned out. The paint removal was tough, it was painted with a two pack epoxy which was very stubborn. Used a wire brush on the power drill to remove the bulk the 80 grade sandpaper for the rest. Finish was OK but not great - should really be shot blasted. After washing in soapy water, rinsing and de-greasing with thinners, I sprayed on a full can of Halfords aerosol primer (in 3 coats).
Now I'm waiting for the arrival of a repair kit for the internal webbing of the gunrack, this is on its way from the US (Weebee Webbing), more to follow.....
More photos of MB365678 at:
http://www.surfacezero.com/g503/showgallery.php?cat=500&ppuser=498

Info at:
http://g503.com/serial-numbers/view.php?record_id=3205

Mechanical PrepPrep 2
Primer