Terrain following in older aircrafts was pretty much a automated business/multi-crew task
I dont remember right now if the early nap-of-the earth flight machines (B-47, B-52 late models, etc) had full terrain following capacity, but in the F-111 and B-1B, terrain following is performed by the aircraft... so, to emulate some sort of terrain following (in night or adverse weather) just planning a very low altitude route and turn on the autopilot (the full one) and you can use the terrain avoidance standard mode as a "monitoring" feedbacks as happens in most cases with those machines, the last requisite is to tweak the aircraft's INI minimum AI level of flight (200 300 or 600 ft) so the autopilot will flight the machine close to the ground/sea.
I never tried this before, but seeing low altitude AI flights, shows that the result is a kind of "soft ride" mode in most cases, but the AI isn't smart enough and sometime it crash into very high peaks. Well, I think that for avoid this, you must monitoring all flight with the terrain avoidance scope to override the AI for that type of "malfuntion", as in the real life.
Is matter to experiment a little bit and do some testing to obtain a usable pseudo-TF mode.