Rust in muffler

[Nascarfastcar]

Got this 90 ezgo 3pg for free the other day. I might restore itm it just needs cosmetic things as plastics, seats, and also needs 1 front hub and a leave spring. Got it to turn spin after playing with the micros in the FnR switches. It's getting 12vs to the starter but it's really slow to start up and has a hard time under compression with the plug in. Brushes inside look new. Ill figure it out later.
But what I really wanted off this was the exhaust. Even though the exhaust tail pipe was broken off I spent the day today fabricating a new tail pipe from images I could find online lol. There was about a 3 inch stub sticking out. The one my current cart has a piece of black pipe I did years ago but I wanted a more stock look on this 1.
My question is when I was welding on this thing all morning and rolling it around. I noticed there seems to be a lot of rust inside. Nothing big or loose just seems like rusty sand. Would this be a problem running it on the cart? I tried blowing out both ends and shaking and every now a then a little cloud comes out. Is there anyway to get it out with the way the baffles are pipes inside? Here of some pics before and after. Its black cause coated it with a cathodic rust arrestor.