Get a 16:9 screen and make a mask for when you want to watch the wider movies. Make a wooden frame and cover it with a non-reflective cloth like Fidelio Velvet - Black 1000. You can get it on amazon.
for wide movies I set the projector to stretch the picture vertically so you use all of the pixels, Then it is shrunk back down to the proper height with a high quality anamorphic lens. The picture is fabulous in both 16:9 and wide screen.
Good luck, the journey to get it set up is half the fun