Apologies if this posted twice.

Contact Cessna. There are factory approved drawings
for a Schweizer towhook installation. There is a charge
for the drawings, but once you own them, you can install
the towhook with nothing more than a logbbook entry.
Since it is factory approved additional equipment,
and not a modification, no 337 is required. I purchased
a copy of the drawings last summer.

Bob C.