We all do trial and error. The only difference is we have more experience to know where to start trying. I also have a coding library to fall back on, places to start, past projects = experience.
Codec is MagicYUV.
For old 8mm film source, even those converted to VHS, I often find that TFM() can be helpful, sometimes even stacked TFM() 2-3 times in the script.
This is something I've run on damaged film before.
Code:
AVISource("e:\Old 8mm.avi")
AssumeTFF()
TFM(field = 1, mode = 5, PP = 1)
TFM(field = 0, mode = 5, PP = 1)
TFM(field = 1, mode = 5, PP = 1)
yadifmod(order=1, mode=0, edeint=NNEDI2(field=1)) # faster yadif deinterlace
I'm not sure you need this exactly, so don't just monkey-see/monkey-do here. It kept as 29.97 (even though source for that script was 24fps or slower). I don't think you have 29.97 discreet frames here, but rather standard 8mm running rates.
Once some of the motion is fixed, you're left with chroma NR and color correction.
I don't have a lot of time to test, but that's where I'd start looking.