While the 133 was supposed to be a replacement for the 600 and 850, I think it was meant to be larger. To me, the centre section of the body including the doors looks like a Fiat 127, so I'd suggest comparing your car with a 1st series Fiat 127. You might also compare your car with the earlier Fiat 127 Fiorino van. (the latest version of the Fiorino is a very different design).
You might also try one of the car windscreen replacement companies (e.g. Autoglass or similar) - they might be able to confirm which other models of Fiat use the same windscreen as your 133 - hopefully these other models would also use the same windscreen rubber.