Drive chain problem

I noticed that my drive chain on my 1980 KZ750 ltd-4 is dragging on something. There is a metal piece attached to the left exhaust pipe and passenger foot peg mount that is causing the chain to rub on the metal piece and push the chain into the sidewall of the tire. I have no idea what this piece is. It looks pretty scratched up from the chain rubbing on it. It is almost square with a hole in the center. The chain looks pretty old and scratched up as well. I was going to replace it but I can't find the specs on what size chain this is. The repair manual says that it is recommended that a chain without a master link be used on this bike. I noticed this chain does have a master link. I would probably replace the front and rear sprockets as well if I replace the chain. I just don't know what this metal piece is and why it's rubbing. Any insight would be helpful. Thanks.

It's possible your bike has a 630 chain. Many riders have replaced the 630's with I believe either 530's or 520's for weight reduction.

You will have to replace the sprockets too as 530/520 chain will not fit 630 sprockets.

I use www.gearingcommander.com when figuring new gear ratio's.

Some sprocket and chain suppliers:

www.sprocketspecialists.com/ (not sure if they are still in business)
www.sunstar-mc.com/home.aspx
www.rebelgears.com/
www.schnitzracing.com
www.jtsprockets.com
www.pmfronline.com

As for what the chain is rubbing on, I suspect a center stand(if you have one)or part of the exhaust system.

I don't think it would be a foot peg support.
If possible include a picture of the chain damage.

Always chain and sprockets together, a set.
Can you post up a clear pic or the problem?