I believe a ball type valve from the local hardware store
would do the trick,

Quite possibly true but not a legal repair.

A look at the FAR indicates replacing the valve is not a major thing
and a 337 is not require; however, the proposed valve is not certified
for use in an a/c.

Look deeper, deeper, deeper into those FARs. Per the FARs you cannot replace a
certificated part with common hardware store parts unless those parts meet
whatever standard applies. If you were to replace the fuel shut off valve with
something not certificated for that aircraft you would need a Form 337 to gain
approval.

I plan on talking with the local FSDO, but until then, can someone
provide any insight into what I'm going to have to do? Thanks, Mike

Another poster recommended talking to Univair. They probably have the part or
know who can get them for you. Is there a Taylorcraft club? Taylorcrafts are
back in production so they probably have fuel shut off valves. Aircraft model
numbers have changed so that the current production part may not apply to an
older model but they might and it would be easier to approve a part from the
current type certificate holder than anywhere else.

John Dupre'