There were multiple studies of using Gemini for lunar landing missions.
Act 1, 1961
While the Gemini program was being conceived, several program plans were under consideration. James Chamberlin of NASA’s Space Task Group was one of the engineers leading that effort.
One of these program plans from the early fall of 1961 included sending a piloted Gemini to the Moon, including options for fly-bys, lunar orbit, and even one with a simple one-person lander. This lunar variant would have required a modified heat shield, deep-space communications equipment, and a redundant inertial navigation system. It was simply a strawman proposal, and was quickly dropped.
Act 2, 1962: Direct Flight Apollo Study
Gemini was still two years from a first flight, but the Apollo program was facing many challenges. Although LOR was selected as the mission plan in July 1962 there were still skeptics. This led NASA to contract McDonnell Aircraft to study direct ascent approaches as an alternative to the Apollo baseline. This report, “Direct Flight Apollo Study”, released in October 1962, included several lunar landing spacecraft designs based on Gemini capsule using a single Saturn V launch vehicle. The report goes into great detail on equipment layout, field of view analysis, mass allocations, etc. The LOR concept persisted, however, and nothing more came of this study (for now).
Act 3, 1964: Gemini Applications for Lunar Reconnaissance
Gemini had not even flown with a crew and McDonnell continued to crank out lunar Gemini studies. This report, “Gemini Applications for Lunar Reconnaissance,” (McDonnell report A634) came out in April 1964. The idea featured a piloted lunar Gemini mission to photograph potential Apollo landing sites.
The overall configuration used a Saturn IB launch vehicle with a Centaur upper stage. This would place a Gemini into a lunar fly-by free return trajectory. An option was considered for an orbital mission as well. An escape tower would be used for launch abort contingencies. Again, this never progressed as there was no money for Apollo alternatives.
Act 4, 1965: Large Earth Orbit
The idea of sending a Gemini to the Moon, or at least to near-lunar distance wouldn’t go away. McDonnell generated “Gemini – Large Earth Orbit” (McDonnell Report B743) on 19 June 1965. It considered two options, both using a Titan IIIC launch vehicle with a Transtage for the trans-lunar propulsion phases. One was to have the Gemini launched separately on a standard Gemini-Titan rocket, while the other had the crewed Gemini launched on the Titan IIIC on top of the Transtage.
The idea never got serious consideration as the top NASA leadership did not want to create a competitor to Apollo. Later in 1966, astronaut Pete Conrad was intrigued enough with this proposal that he managed to have a high apogee excursion added to his Gemini XI flight.
Act 5, 1967: Lunar Rescue Considerations
After the deadly Apollo 1 fire in January 1967, Gemini variants were considered as rescue vehicles should an Apollo mission experience an emergency that precluded a safe return to Earth. A McDonnell presentation, apparently an in-house study, described three Gemini rescue configurations. They evaluated scenarios for lunar orbit rescue, lunar surface rescue, and a lunar surface survival shelter. The package has the title “Lunar Operations Rescue Considerations” but has no report number nor contract number. Some scale models were built, and these are seen at the top of this page.
Some details were never addressed in these studies such as communications antennas nor crew ladders to the surface. The earlier (1962) studies had several concepts for how the crew would view the surface during landing, while this 1967 study report and photos of scale models related to this study had no indications of what technique would be used. These rescue options were never pursued, as any additional resources were felt to be better spent improving Apollo reliability.
I chose to build a model of the lunar rescue version at it might appear on the Moon. As mentioned above, the ladder configuration and antennas were all conjectural.