63 Dodge Dart, now let me see;)

You're doing a good job on it. 2 different colors of the high build will show you high and low spots if you use one color this time and the other color the next, switching back and forth between coats. I learned to feel for them instead of just looking at them. Use the hand you don't write with to lightly skim the panel, with primer dust on your hand. You'll get the hang of it after a little practice. Once you feel a place, take a pencil and lightly mark back and forth across it and then sand across it with a long block. Pencil tracks will stay in the low spots and disappear on the edges of it. Did you find a 4 speed hump?