[TL;DR] You can 1) use VTS Timeloop 2) use NASA's eyes on the solar system to visualize terminators on other planets at any time.
1) VTS Timeloop + Orekit
Instead of computing the terminator myself, I prefer to rely on visualization solutions such as the VTS Timeloop software from Spacebel/CNES which allows to visualize planets and space missions, offering a 2D view (usually for ground tracks) and a 3D view (using Celestia). It is not open-source but downloadable for free.
I modified one of my past projects to be able to visualize solar system planets from 1957 to 2057: https://github.com/GorgiAstro/planetary-timemachine. Instructions are available in README.rst. The VTS project is currently configured for Mars at 1976-07-24T10:35:26Z.
For Mercury, Venus, the Earth and Mars, a WMS layer is configured for the 2D view, which means that higher resolution imagery is available when zooming.
More about SPICE and planetary ephemerides:
The planetary ephemerides in VTS are defined via CIC files, which are basically CCSDS AEM and OEM files with a few differences. To visualize Mars back in 1976, I had to override the default VTS ephemerides though, which I did using the Orekit library instead of having to deal with SPICE kernels myself.
2) NASA's eyes on the solar system
I realized afterwards that this NASA software provides access to historical data of planets and interplanetary missions.
Just browse to 1976 and see Viking-1 orbiting Mars. The SPICE kernels are probably downloaded on the fly, so if Mars does not seem to rotate within a sol, it means that the SPICE kernel is still loading.
See some pictures below. The lighting effects on the terrain near the terminator look quite realistic. Although to answer the OP's question, the terminator location is not clearly marked here.