The hubs look like the 3-piece Campagnolo: are they steel centers with pressed on alloy flanges? If so, that would place it in the 50s. I'm not sure the yellow is original; I've seen red and blue ones. I don't think the brakes are original, and probably not the Simplex rear either.

I have a similar blue one with Gran Sport deraillers and Ballia brakes, same steel crank.

You could get the decals on ebay, but from what I've seen they're based on a low-end 70s bike boom model.