I have my 312 stripped down. The timing chain is as loose as anything.
I plan to replace it, along with the sprocket.
Q. Rock-Auto who I use for parts supply state the chain has 56 links. Correct ?
I counted the number of links on mine and found 28.
Is the 56 because the chain is double thickness. ie, 2 links wide?
Picture taken in 1960. Funnily enough it still looks like this! 
1959 Mercury Monterey 312 Y Block. NORFOLK, ENGLAND, UK.