I remember way back when i used to do this before ( 20 years since ), painting the model pieces ( some still on the racks ) before assembly.
But now i'm older (wiser ?) i have a question.
If you paint two pieces and then try to stick them together surly you'll be sticking paint to paint, and the Poly Cement will have nothing to "melt"
So what's the expert solution ???
Zardos