I think I read somewhere that often, in the field during the war, if the plexiglass noses where cracked or broken or otherwise holed, rather than wait the 'two weeks' for a replacement, the ground crews would fashion an aluminum replacement from scrapped aircraft on the base.
Also - since .50 cal machine guns and ammo boxes were as plentiful as rain - those new aluminum noses would be ported for gun barrels in all kinds of configurations.