Other people have addressed the chain wrap, derailleur capacity, and chain wear concerns, but I feel I ought to clarify this bit:
Originally Posted by
austinbikebill
Is my drivetrain so old that I need an even beefier single speed chain?
A single-speed chain, with rare exceptions, will not work on a derailleur-equipped bike. Single-speed chains are 1/8" wide, while derailleur chains are nominally 3/32" wide. Those designed to work on rear clusters with eight or more sprockets are even narrower. A 1/8" wide chain will not be able to seat properly on a cluster designed for 3/32" or narrower chain. When replacing a chain for such a cluster, you need to get one designed to run on the number of sprockets your cluster has. You can generally use a chain designed to run on a higher sprocket count than what you have, but not vice-versa. The higher sprocket count chains tend to be more expensive, so you may as well use the one designed for the exact sprocket count of your cluster.