Only time you need a 1/8th chain would be if you're running a 1/8th cog or 1/8th chainring.

When you say "non-****ional" gears, what exactly do you mean? Broken derailleur?
Like others have said, I would try to get the bike functioning as a road bike, sell it, then buy a fixed gear bike as a starting point.

The Zurich is one of Lemond's better bikes with 853 steel!
Unless the bike was stripped, it shouldn't cost that much to get that bike in a good condition to sell.
You could most likely get $500+ for a bike like that depending on the condition.

Lemond's have a large following and the Zurich is a desirable model.

With that money you can buy a fixed gear bike and have everything ready to go from the beginning.

I just don't see the reason to screw up a nice road bike.

You can pick up a steel Fuji Feather for $500 Fuji Bikes | LIFESTYLE | URBAN | FEATHER
or aluminum Aventon for $500 https://www.retro-gression.com/colle...-complete-bike

By the time you've spent the money to make the Lemond a proper single speed, you most likely could have spent the same to get it back to running order so you can sell it.