Welcome!
Some swear by Mr. Surfacer for primer coats, light filler and rough surfaces. I find it difficult to dilute and the strong chemical smell is worse than Plastic Solvent Cement! Yet some applications its the best choice.
1940-1950's PR aircraft eh?
Many surplus WWII aircraft were stripped of camouflage paint and used for this in Canada. Also these aircraft were used as trainers, search & rescue missions and some modified to become water bombers. One build on the back bench I have is a NMF Spitfire flown across Canada in 1946 for PR events.