So I was told recently that even if the pattern of the driveline matches that of my crank, I still need to run a PTO. Is this right? I thought they were used as an adapter when the patterns did not match.
No you don't. bolt it directly to the crank over the flexplate using the same allen bolts that would normally hold the PTo Adaptor. Here are pics of 2 different 1310 drivelines, one using a PTO adaptor and one that dont use one. Funny, both came from the same boat..........my twin jet.........

,......Funny thing is, the slight difference in length makes then exactly the same with the PTO adaptor on the one.
If it's a Ford though, carefully line everything up, there's one offset hole on a 429/460 crank.........gets me in trouble every time.


Ray
EDIT:: Frank, using one WITH a PTO adaptor gives you the advantage of being able to disconnect the driveline fairly easily to run the boat on the hose. You'd sooner stick your privates in a beehive than get the direct hookup off to do the same, if at all.........just an FYI............