[Buster]

You're lucky that you've gotten the unsprayed undercarriage.
The black undercarriage looks good on the internet pictures but in reality it is spraying work worthless because the paint falls off.
The black undercarriage is sprayed without prior degreasing, sanding or base coat.

Before you take on the real job remember that the undercarriage is not suitable for heavy duty.
After the undercarriage from my Kat was pretty twisted I have completely taken the undercarriage apart and reconstructed it with the addition of a lot of solid aluminum.

I can tell you much more about the Kat undercarriage but it is much more fun when you discovered it yourself and tell us about it.