1981 750LTD exhaust questions

I have a 1981 750LTD and the exhaust is rusted on the bottom of the megaphones and the glass packing is long gone. The pipe that is supposed to come out the end is also gone.
Has anyone been successful in opening up the pipes and affecting a good repair? If not, do you think it is possible to grind the welds off, remove the factory muffler sections and install aftermarket slip on mufflers?
I have a brother that is a journeyman welder and another that is a machinist so I'm thinking this is a doable project. I really want to keep the factory look and keep the bike as quiet as possible.
I'm thinking of having the ends cut open with a plasma cutter, repairing the rust holes in the bottom and then making a new baffle and installing mounting tabs in the end of the pipe so I wouldn't have to put any holes on the outside for bolts.

I don't know if the internals of the KZ750 muffler are similar to those of the KZ650, but the KZ650 has quite a bit going on inside. The image below shows what I mean. Ed

That looks like what is going on in my pipes. Do you know if the factory pipes had glass packing in them?

Glass packing? probably not.

My RH muffler broke off completely at the weld. weld C in the pic from eebbaayy.

Here's a 750H muffler system showing one of the baffles. my muffler broke off completely w the baffle still inside of it.

I'm thinking if I ground weld c in the above image on my pipes, I could use aftermarket megaphones and keep the stock look (if I can't repair mine.

The stock LH muffler has a recess for the center stand. One potential problem is that aftermarket don't have the recess & the center stand will bang against the LH muffler. Some guys modify the center stand or stop so that the stand won't hit the muffler, but doing this lowers the center stand & it could scrape the ground while turning. so not recommended.

The center stand never crossed my mind. I will definitely try gutting out my factory exhaust and repair it first. If that doesn't work I may need to look into a complete 4-2 aftermarket system.