Swing arm wear strip

Please consider this proposal and provide advice.
77 KZ750B twin runs reasonably well but there is a pretty significant vibration from the drive train. I've researched this a bit and discovered this is normal if no mechanical problems are found.
I've discovered that leaving the chain quite slack - three or four inches of travel between high and low- really helps reduce this phenomenon.
The down side is the chain rubs against the swingarm.
I've had dozens of bikes- they all had some type of wear strip in this location. This bike has none.
I know I'm not the first to want this improved. Should I fabricate something? Has anyone else tried this?
Ideas?

I'd say that four inches of slack is dangerous. There is a real possibility of the chain coming off the sprockets and locking up the rear wheel.
You say that it runs reasonably well. That suggests to me that something else needs attention, and that running so much slack is just compensating for an unaddressed problem.

Yeah, you shouldn't have more than maybe 2.5 inches of slack from high to low. A vibration from the drivetrain is more likely caused by something like the rear wheel being out of balance.

I would definitely recheck things like valve clearance and carburetor synchronization to rule them out.
I would then carefully scrutinize motor mounts to be sure they are properly tightened, and swingarm bearings or bushings for looseness, and wheel bearings and shock absorbers. Is the cush drive in good shape?

How many miles on the drive chain? Any stiff sections in it?

Malcolm wrote: Please consider this proposal and provide advice.
77 KZ750B twin runs reasonably well but there is a pretty significant vibration from the drive train. I've researched this a bit and discovered this is normal if no mechanical problems are found.
I've discovered that leaving the chain quite slack - three or four inches of travel between high and low- really helps reduce this phenomenon.
The down side is the chain rubs against the swingarm.
I've had dozens of bikes- they all had some type of wear strip in this location. This bike has none.
I know I'm not the first to want this improved. Should I fabricate something? Has anyone else tried this?
Ideas?

Are you kidding us???? Holy cow, that definitely is NOT normal! You need to identify and correct the problem, and believe me leaving that much slack in the chain definitely is NOT the solution! I urge you not to ride until you really fix the problem as doing so may get you seriously hurt.

Notice the clip below from the KZ750 Twin Kawasaki Service Manual specifies 25 -35mm = 1.0 - 1.4 inches of drive chain slack. 3 - 4 inches is WAY too much slack! Ed

Yeah that's not going to work.
The assembly is mechanically sound, square and aligned. New chain and sprockets. The risk is zero.
Vibration and noise in mechanical systems is stress. I've got quiet and smooth.
Thanks for your replies but you'd agree if you were me.

No I wouldn't. Believe me when I tell you that your bike was not delivered new from the factory with anywhere near 3-4 inches of slack in the chain. Instead of ignoring the problem (and it IS a problem) I highly recommend you take a look at the Kawasaki Service Manual and try to identify and correct the problem. If you are unable to do so then you should take the bike to a motorcycle shop and have them diagnose and correct the problem. Again, 3 - 4 inches of slack in the drive chain definitely is far too much and indicates that there is a problem that needs to be corrected. Ignore my advice if you like, but just so you understand, I have owned, ridden, and worked on motorcycles for 54 years so I write this with a fair amount of experience under my belt. Ed