As Jacob mentioned, the high Atlantic fiberglass sails were retrofitted on several of the previous Guppy conversions. Many of the Guppy operations were in the northern Atlantic and Pacific oceans, where wave heights could easily swamp the bridges of the two earlier step sail versions. The fiberglass was over a metal framework structure, with the bridge structure raised to the top.
An easy distinguishing feature between Guppy III’s and the earlier Guppy’s that received the Atlantic sail is that Guppy III also received the three PUFFS sonar fins on the upper deck. A more subtle feature is that they are 15 feet longer, due to a hull plug inserted forward of the control area, housing a more extensive sonar electronics suite.
The last surviving Guppy III, Clamagore, is to be sunk as an artificial reef for divers. It has been poorly maintained by the group at Patriots Point in South Carolina. Lots of corrosion and missing parts topside. The interior is in surprisingly good shape, however. Some sub vets have been trying to save her, but the group at Patriots Point seems determined to sink her.
I visited there two years ago and photographed it with my Nikon DSLR. I subsequently wrote an article for the SubCommittee Report, which can be accessed at this link on Navsource:
https://navsource.org/archives/08/pdf/0834331.pdf Lots of color exterior and interior photos, and I have many more. I have the resin Clamagore kit which Yankee ModelWorks put out years ago. It has the PUFFS and the plug. I will be using an old Tom’s Models Guppy III sail, which has more accurate features. Right now, my Guppy IA Becuna needs only a dull coat to complete it.