Joined: Jan 2010
Posts: 9,809
Likes: 1,783
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
I assume the Trek has a Huret derailer.
Remove the Allen screw from the reverse side/end of the derailer mounting bolt and the bolt will spin free.
The Treks all have Campagnolo-style derailer hangers, so accept all modern derailers, including all Shimano direct-mounted derailers including the Light Action.
Shimano derailers having a mounting "claw" are not what you want to use, unless the claw is removable, which it usually is.