Quieting Older Generator

I was given a old 5000 watt Coleman genreator with a old cast iron L head engine. It is built like tank but BOY is it loud under load with just the small muffler. Anyone mounted a canister/automotive style muffler on a gen set like this to quiet it down.

I mounted a muffler of a 350 yamaha on one of my generators and quieted it right down. Even under load. Found the muffer at a yard sale for $2.