Without knowing millivolts-per-megapascal it is impossible to do what you want. The manufacturer's datasheet can tell you. Or you experiment with known pressures and take readings at each different pressure.
While it is fun to play with old salvage equipment, if I actually want to know a pressure, I will buy a new sensor that has a datasheet. I will buy it from a reputable retailer that has stock so that next time I want to buy the same sensor I don't have to find their eBay listing again.