Thing about using the proper tool is by screwing into the Derailler mounting tab It is not bent across the threaded hole.
Shimano and Campagnolo pro tool sets also have a tool like that ..

A bike shop will do the task for a few bucks. Index schemes demand the derailler tab is in a plane
perfectly Parallel with the frame center line measured by seeing that the tool has an equidistant relationship to the rim thru a 270 degree swing of the long arm of the tool .. fore /aft-up /down.

Just bring in the bike as is with the wheels on it and It will only take a minute.