The 500T is essentially the same bike as a DOHC 450 - it's basically a stroked 450. With looks only a mother could love, and less performance than a 450, it was not a hit with the public, and not a big seller. The general thought is that Honda should have gone to a 650 or larger twin with the 450 concept - but in those days everyone was 4-cylinder crazy, so.....
Your concerns about cam chain tensioners is misplaced, to a large degree. You do need to keep them in good tune, which includes cam chain tensioner, but it's not a tragic weak spot or anything.
In general 450's are as durable as any bike Honda made (other than Gold Wings).
The K0 (Bombers) are substantially different than the 5-speed versions, and parts are really hard to find.
Mostly you just keep the carbs clean, change the oil frequently, and enjoy them.........