My original answer probably looked something like this:
The audio you have is not very good, even partially restored by us, because your captures had problems. You should re-capture the video in mono mode on the VCR. Only then will it be the best it can be. The fluttering/buzzing noise in your audio now makes the video almost unwatchable.
5 - Your audio workflow, on these smaller files, should be MP2 to WAV, before processing. This can be done several ways, be it Besweet/BesweetGUI, Goldwave, or FFMPEG/HeadAC3e.
6 - You'll need Goldwave too, it has some filters that operate different from
SoundForge. It depends on your exact audio file. It takes practice.
7 - You'll need to convert your audio back to MP2 or AC3, WAV is too big for DVD (wastes space), AC3 is better than MP2 for NTSC (MP2 not officially supported in the spec), and FFMPEG is one choice. Others include the authoring software (but I don't think DVD-Lab has this option), or Besweet/BesweetGUI. The guide made for you, found on this site, is for HeadAC3he/FFMPEG to do the MP2>WAV>AC3 method.
The long 3-hour tape is just going to be done like one long match or episode, as it should have the same noise profile throughout its duration, unlike your mix-and-match recordings that were all over the place.