I wanted to update with what I ended up doing today.
While I had the carbs off, I swapped in the manual adjuster. I would like to say first that I quickly found out that moving the o-ring seal back out of contact improved the "feel" by eliminating the majority of friction in the assembly. All you have to do (BEFORE you install the tensioner) is to turn in the bolt by hand with the lock-nut backed off. This will slide the o-ring clear of the body of the tensioner. Once it's clear, you can gently slide it farther out of the way. Try to avoid cutting the o-ring on the bolt threads. A shot of WD-40 will help.
Once I could feel what I was doing, I turned in the bolt using fingers only. It felt just like you would expect for a system using a silicone/rubber tension roller. That is, no clear "tight point," but just a smooth increase in the effort required to turn in the tensioner bolt. I settled for turning in the bolt until I felt first contact, then just a bit more, perhaps 1/4 turn. I then tightened the locknut. I figure this will give a slight preload on the tension roller, without crushing it so much that it wears out prematurely. I'll recheck the tension after I run the engine in a bit.
Speaking of wear on the tension wheel, does anybody have a gut feel for how many mile/years the roller would be expected to last in the real world? I have no reason to believe the one I've got is not the original, which would put it at 5600 miles and thirty-eight years. I haven't looked in the Service Manual yet.
Richard