Im with norm, once i say that ruted out flange i was thinking that the water possibly went right down that exhaust or into a leaky flage or hole in the pipe etc.
Sure hoye dosent have that flange? looks just like the original one that i thought that hoye would have. Ask if they have a parts tractor with it on it, they have parts tractors for used parts, but you have to call and ask.
If you can take all your rusted pieces to a custom muffler shop they can make something up to match the original, i would go to tsc and buy a small mufler for a cub or some othersmall tractor, or one from hoye for that size tractor so that you dont end up with something fabricated with an auto muffler on it. But hey the mufler off something like a jetta or civic or ford aspire or even the chamber at the end of exibitions or surburbans would probly work and maybe cheap[er.