TOPIC:

I don't think the tensioner has been replaced in my 86 ZN1300. I know that folks have used tensioners out of another Kawi model and used manual tensioners. What the consensus on the preferred method and which tensioner to use these days?

I used the APE manual tensioner. Inexpensive and generally considered foolproof. No mods or messing around required. Easy to install and adjust. Once its done right it should be good for thousands of miles before another minor adjustment.

Ive seen a million posts about the cam tensioner replacement mod but ive never seen any detailed write ups with step by step illustrations.

To complicate things, it seems like my 86 has some sort of factory 'hydraulic assist' (for lack of a better description) tensioner - not clear if it even needs to be replaced ????

AS far as I know, you're the first to question the hydraullic tensioner and kudos to you for wondering if it's a problem. I can't remember any posts regarding the hydraullic tensioner. So lets talk about the "problem" with the design of the tensioner.
The earlier KZ tensioner has a spring which mechanically applies pressure to the tensioner system and the locking ball system holds the tensioner at that position. What happens with this tensioner is the locking balls tend to chatter and wear notches in the tensioner rod to the point that if /when some excessive force from the cam chain under rapid acceleration / deacceleration will cause the locking balls system to fail and allow the tensioner rod to retract which will allow the chain to gain enough slack that it could slip on the camshaft gears and then we get the bent valves syndrome.
The hydraullic tensioner replaces the spring with pressure via a piston and engine oil pressure. The rest of the tensioner is the same as the mechanical tensioner. The hydraullic tensioner still has the locking ball system which is the component which has failed in the past. I would consider replacing tha hydraullic tensioner, although there appears to be no recorded experience with a failed hydraullic tensioner. It's possible that Kawasaki engineered a cure for the failing locking ball system and I would guess that you're really looking for information regarding any possible experience with the hydraullic tensioner.

I'm putting up this post to put some light on why the tensioner is questionable. How exactly this info is relevant to your concern, I'm not sure. If I was in your position, I would pull that tensioner out and inspect the tensioning rod and see if you can see any indication of chatter on the tensioning rod. It will look like indentations in the rod as if the locking balls had been hammered in to the rod. Note- when /if you pull the tensioner out, it's possible that the cam chain will slip and the camshafts will have to be retimed. So my caution here is that you can't just pull it out , look at it , and then put it back in thinking the chain didn't move. It's really important that you check the camshaft timing if you do pull it out and reinstall.