Coil clearance isnt critical......most advice says use a dollar bill folded once,a business card,or a .010 feeler gauge.
I suppose I wouldnt argue with any purist who says paint on the fins would affect their ability to radiate heat to some extent.I have painted a couple of my engines with hi temp engine block paint (Cummins Diesel Green!) with no noticable affect although I didnt use a temp probe before and after.....