adjusting rockers....augh

[John bouy]

I'm re-assembling the top end on my 94 mercruiser 4.3l and am trying to figure out how to adjust the rockers. It's hydraulic lifter and I've tried setting the preload to zero lash plus 3/4 turn (what the book says) but after 10 mins of running the nuts rattle loose. It doesn't look like I have locking nuts and I've also heard that they could be non-adjustable where you just bottom the rocker out and torque to 20 lbs. It only says to torque down like this if you have a motor with a "balance shaft" which I don't have however I talked to a guy at my local machine shop who says that the nuts are non locking therefore I should torque them down this way.... The mechanic at my local marine shop says otherwise that I should set them the zero lash + 3/4 turn method.

So my question, should I replace the nuts with proper "locking" rocker nuts and set the 3/4 turn Method or do I keep the same non-locking nuts and bottom the rocker out/torque to 20 lbs.
is there any way to tell if these are adjustable or non adjustable rockers?

 

[Bt Doctur]

do you have an engine serial number

 

[John bouy]

I got serval different opinions and found out they are non adjustable. Torqued down and everything works. Runs like new!
Thanks for the reply though.