In order to determine the number of drive links in your chain you need to confirm the bar length and the pitch of the chain. Many of the McCulloch 10 Series saws used a somewhat unique .354" pitch chain which requires 61 DL on a 16" bar where 3/8 chain requires 60 DL. You also need to confirm the gauge of the drive links, as they used both 0.050 and 0.058" thick drive links. You also need to confirm the sprocket on the clutch matches the pitch of the chain as it was a common mistake to try and use a 3/8 sprocket with .354" chain and vise versa.
The good news is there were literally millions of those saws built, and the later 600 Series saws (PM610, PM605, etc.) used the same bars and clutches so there are lots of parts available and most saws were switched over to the more common 3/8" pitch chain at some point.
40:1 with a good quality modern oil will be just fine.
The impulse operated automatic oil pumps on the 10 Series saws are more tolerant of oil viscosity than modern saws with gear drive pumps. Any modern, good quality bar oil will be fine. It is always a good idea to use a lighter weight or winter weight bar oil when the ambient temperatures are below 40 or 50 degrees F.
Mark
