This is a bit of a stretch, but potentially this could be Arthur C. Clarke and Stephen Baxter's The Light of Other Days
The technology here is the WormCam, it is a remote viewing wormhole that allows one way information travel. The opening scenes show the tech being used to steal political secrets, about 1/3 of the way into the book a demonstration is used of a remote viewing of Saturn eighty light minutes away a huge step up with the technology that then allows for a similar wormhole 'setting' where the location is still on earth, but now looking into the past.
If I restrict the spacelike interval to a couple of metres the rest of the wormhole span becomes timelike...'
And the first demo shows the lab eighty minutes into the past.
The tech scales up several times during the story, in capability and in convenience.
This is absolutely not something you could have read in the 70s being published in the year 2000. But the direct juxtaposition of viewing remote objects in space and then the past made this seem a potential match.