Any thoughts on how to prepare these exhausts for painting?

Also, on the opposite side exhaust group, I chipped off a piece while drilling; I added a ‘smidgen’ of Milliput Superfine White formed around an inverted drill bit, to keep the opening. I need to add another fill layer, and I wonder if I should close the opening and drill out the Milliput?
Here is a sketch of what happened:

The exhaust looks like this now:









