Sadly now my engine is back in the car, my supposed air cleaner has been found to be too big.
I have gone to the trouble of painting the one I bought off eBay. Sadly it is too big and the bonnet (hood) opening mechanism fouls it making it a bad fit.
It was a 1958 air cleaner, but I assumed it would fit the 1959 model Mercury. Apparently not. 
Does anyone have the correct original? I don't mind some restoration work on an untidy one.
I don't want a chrome fancy one.
Picture taken in 1960. Funnily enough it still looks like this! 
1959 Mercury Monterey 312 Y Block. NORFOLK, ENGLAND, UK.