The Gemini spacecraft, with modifications, was also lunar-orbit capable in theory.
See the Gemini lunar-orbiter that was proposed by Grumman engineers back in 1961 at www.astronautix.com.

If only JFK had known, and James Webb and WVB had accepted that idea of adapting the Gemini-spacecraft to fulfilling JFK's dream.
The Gemini, with a doubled heatshield, and with a few deepspace nav-devices,
would have made it a successful moonrated spacecraft that could have successfully linked up with an orbiting LH2/LOX fueled Centaur-stage
to blast it to the moon, as early as 1966 or 1967.
What might have been!

Of course, the result of such 'hypothetical events' could have been that the Soviets would have ended up so humiliated by being beaten to the moon by a couple of American Gemini spacecraft by or in 1967 [the Soviet's 50th anniversary year] that Brezhnev
could have ordered the Soviet spaceprogram to go ALL OUT [money and resources no object] to send Soviet
cosmonauts to at least loop around Mars
in 1976 [your American bicentennial year] and return safely.

Jacob