Ah yes, that would be the Mike Jensen STC, which eventually went to Penn Yann (who improved enough details to get a new STC), and thence to A.E.R.O. Don't know what happened after they were bought out recently.
There was a string on supercub.org several years ago, viz:
https://www.supercub.org/forum/archive/index.php/t-34802.html
If you'll indulge me for a bit of a history lesson: Mike Jensen was Dave Johnson's son-in-law. Dave had started the whole 180 Supercub thing with Field Approvals, for towing gliders at the old Black Forest Gliderport near Colorado Springs, and was the glider tow contractor for the Airforce Academy for many years. Dave was, ummmm "frugal", and would find economical ways to do things. Like scrounging up orphan engines. At least one of his 180 'cubs that I flew was converted from an "HO" version ( NOT the model railroad gauge...) to a standard version, but I forget which. Mike developed the multiple STC, which regularized the process, and cleaned up some of the small details which were what I'd call "field expedient", and issued a proper set of drawings and instructions, and some parts and materials kits. As I recall, it could be done with either an 0-360 C2A (conical mount) or 0-360-A3A (Dyanafocal mount)--think Cherokee 180. The biggest performance limitation was the Sensenich 76EM-0 prop, typically a 54 or 56 pitch. It's a decent prop, but doesn't pull as well as the McCauley "Pawnee" 235 series prop (?82-52??), or the "Scout" FA-80-42 prop, both of which require extended MLG and/or larger tires for tip legal clearance, and both quite a bit heavier than the Sensenich. They DID run on the hot side of OK with long slow tows at high density altitudes, with stock nosebowl oil coolers. The stock muffler system was a bit of a recurring maintenance issue too, and not very efficient. The other limitation of the Dave's and Mike's conversions was fuel flow on the larger engine at high angles of attack, which lead to a "takeoff of left tank only" and left tank usable capacity of 9 gallons limitation, since the left tank feeds the firewall hedder tank, and the right tank the aft hedder tank. I doubt that ANY operators ever violated those restrictions.... One could probably do the STC for larger fuel lines and "both" positions.
I flew a couple of 'cubs with the Dynafocal installation, and while they seemed smoother, some of the sheetmetal and other bits seemed to suffer from the movement and shutdown "shake" from the looser mounts. A different engine mount would be required.
Circling back to Patrick C's original question, your STC provides your options, unless field approved otherwise. And in my experience, there's really nothing wrong with the narrow deck engines, they're still supported. Both the C2A and A3A are very basic, solid engines. IF your core is OK, why not just do a first class overhaul on that? As to props, again, unless updated by Penn Yann (which I think they eventually did), that may be a limitation. Skywagon8A suggested that IF licensed in "Restricted--Banner Tow" there may be some more leeway, although prop clearance might still be an issue. I'd check with your friendly local FSDO for a more definitive current interpretation.
Patrick, hope it all comes together well for you.
Thanks. cubscout