26 in, did not do the TW
N3110J - Private Maule MX-7 series Super Rocket at Perth - Scone | Photo ID 248353 | Airplane-Pictures.net
When you fit an STC, you need to fill out a 337 form and submit it to the local FAA office
I always thought an STC was like a pre approved modification whereas a 337 was a field change that required individual field approval fro the FAA.
I will pull back out the paperwork and reread it