Earl C. Reed

The Reed conversion only covers the 65 and 75 hp Continental engines. The Reed conversion also limits gross weight to 1100lbs. Of course all of this is detrimental to usefulness of the airplane.
ScootAir has an STC for clipped wing Cubs that allows 85 and 90 hp Continental engines. The STC raises the gross weight to 1220lbs (when properly modified to proper configuration).
The Univair STC is the only multiple use application of an O-200 on a J3 (clipped or otherwise). Legal O-200 (100hp) Field show more Approval (337) installations on J3's, while there are some, are few and far between. JimC/Rick Rice was one of those. Most of the 337's I have seen, limit (by dubious means) the O-200 installed on a J3 to 90 hp. https://www.supercub.org/forum/archive/index.php/t-47636.html

The Reed Clipped Wing version of the J-3 was flown as an airshow mount by many of the performers of the 1950s. In this modification, about 40 inches are removed—not from the tips, but from the roots of each wing—in accordance with the Reed Aircraft Modification Manual. This modification allows operation in the FAA Standard Category. https://www.piperflyer.org/featured-articles/item/940-piper-cub-the-reed-clipped... show less