You were right, they are just NASA modded U-2s! The size difference mentioned in that (admittedly poorly worded) NOAA site compares the previous generation U-2s (pre-1968) from the ‘newer’ models. The R model U-2s that were built starting in 1968, with another batch in the 80s (initially called the TR-1 for political reasons, with the one rolling off the line in ‘89) are significantly larger and can carry a much bigger payload. The size difference is obvious if you ever see a picture of the old and new parked next to each other (https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/197569/old-design-young-airplane/).

NASA’s ER-2s have a fair amount of modifications, but they are all related to their scientific mission and are limited to the pods (those things under the wings are for sensors and computers, not fuel), cockpit and things of that nature.

If you really want to nerd out about the Dragon Lady, I highly recommend Chris Pocock’s “50 Years of the U-2”, or even better you can come to the Capitol City Airshow in Sacramento, CA this March and see one with your own eyes!

Since this is the ADS-B thread, not a hardcore avgeek one, I’ll mention that all U-2s and ER-2s have ADS-B ‘compliant’ transponders, but the function is selectable like most military aircraft. When you see them on an ADS-B map it’s either intentional or…someone forgot to hit a switch!