KZ440 Exhaust rust/prep for aftermarket slip-ons

I am looking at putting a set of aftermarket slip-ons on my 1980 KZ440 and want to clean up exhaust while im at it. Most of the headers look like they just have surface rust but where they have they are welded to the muffler and cross pipe looks a bit worse. Both sides of the exhaust have a leak and I'm assuming its the black mark coming from the weld. Ive attached some pictures.

So my questions are:

• What is the best way to clean up the surface rust on the headers? I've read about steel wool and vinegar working.
• what should I do about the bad rust on the bottom? Is it worth cleaning up?
• What can I put on the pipes to stop the exhaust leak or will it just need a new weld?

The slip-ons im looking at are the Emgo shorty mufflers: www.dimecitycycles.com/chrome-17-inch-sh...gaphone-muffler.html

Any help is appreciated!

Is the motorcycle running yet? If not, running the engine may burn off some of the rust n stuff. If you've already had the engine up to full operating temps, then I would remove & disassemble the exhaust system, then just start cleaning to assess its condition. I would use soft brass wheels on the rust. The blueing/discoloration is probably permanent.

This is kind of different, but I refurbished a very good muffler system by using soft brass wheels on the rust & cleaning the insides by various means. bubble brush car wash. evaporust. carb cleaner. brake kleen. After plugging the openings, I left the evaporust inside the mufflers for a week or two. I forget exactly how long. The stuff has detergents & rust converter chems. Afterwards, I sprayed the manifold/crossover section & the insides w silver Rustoleum bar-b-que grill paint. I was kind of expecting the paint to at least peal off the chrome, but it's still intact. and where I can see inside thru the muffler tip openings, ditto.