Uli, I have done this conversion on three Pawnee's that I have owned, and for the life of me I am still at a loss of words as to why others have not done this. The handle is the hopper dump handle standard on all Pawnee's it extends from below the floor and rises up to a position about three feet above the floor. I is a double connected bar that has a bushing and it is fitted in two places.
The lower end has a slight bend facing forward for the hopper release to attach. Since we have no need for the hopper I removed it and incorporated that handle as the tow release handle. I cut and welded the lower end to face backward to connect to the tow release cable. This handle is extremely strong and the leverage is unequaled compared to other releases. The most important aspect is the location, just forward of the throttle and mixture handle within easy reach in the event of an emergency. IMHO the Schweizer hook is not the big problem, but reaching the release while positioned on the floor is the main culprit. Just strap yourself into a Pawnee and try to reach the floor panel, not an easy thing to do. Now put yourself into an emergency situation and it becomes even more difficult!
I will be glad to snap a few pics and send them to your email address. Bob

Bob,

The reason "others" haven't done what you did with your tow plane is that "others" have not found themselves pointed at the ground and unable to release while towing an inadequately prepared student pilot or any glider pilot not responding properly to losing sight of the tow plane. Once this happens to those who can make things happen at any club or commercial operation, changes will be made posthaste.

Any tow plane without a release handle available to the tow pilot sitting in the upright position is a disaster waiting to happen. The FAA and SSA know the recommended release handle (five to one ratio and located down on the floor of the aircraft) when combined with a Schweizer release is inadequate, they both mention this in their advisory circular and in the SSA literature IN BRIGHT RED LETTERS. Lack of mechanical advantage can be corrected, the movers and shakers need to stop waiting and start reacting.

Walt Connelly
Former Tow Pilot
Now Happy Helicopter Pilot