2nd what Ssrjim says - one of the touted DeKupps system benefits is "spraying at any angle".
I can't speak to how well it works, but I am in a similar situation. Painting the frame of a 1950 2-ton, literally the first thing I've EVER painted with a paint gun. Gravity feed HVLP. My first run was caused because I dripped paint out of the vent hole!
Trying to paint the bottom of the frame is awkward, at best. You can physically cover the vent hole with your finger to prevent the leak out, but without a mostly full cup, you're still highly limited on the angle.
The DeKupps aren't all that expensive at Eastwood, and their are adaptors for nearly any gun, apparently. Check it out.
-Michael
