Maximize the frame and fill the entire screen, change the gain temporarily so the peaks are exactly the same size, and eyeball it, using your eyes and ears to zero in on the general area.

I've never done it, but what i would try is to batch process all the audio tracks to maximize the audio contrast, to make it easier for the synch algorithm. Normalize is the easiest, but maybe you've already done that. Some nonlinear amplification may be combined with some filtering/ equalization. it may help create more contrast in both amplitude and frequency domains.

after (hopefully) successful synch, just replace with the original audio tracks.

maybe not all the tracks, it could be too much work for the experiment, but at least with the tascam track

Done!!!

@DrDave I did as you (and @dtr) suggested ,-) problem was recordings were spacially different; while Tascam was static, cameraman was moving around like a cockroach, je je. If you add to that the nature and amount of the sound and own limitations of recording devices you get Dr Jekyll and Mr. Hyde waveforms. Anyway, I tried to adjust audio levels but what helped the most was to EQ both audios to a specific frequency and then pan them L&R and manually sync with a couple aspirins. Curiously first clip was the last and hardest to sync. Not 100% accurate but will do =)

@Alienhead that was what I first tried, but in this case was worthless, both merge and sync options.
Me likey temperamental ;-) Un abrazo amigo

@kankala are you cosins with mahakala? :P As I wrote above, EQ the audio to 4Khz greatly helped focus on the syncing process. What I also did is cleaning the myriad clicks and inner distortions of Tascam's recording.

You guys rock XD, @DrDave , @Alienhead , @kankala and @dtr thank you so much

gashô

PS
When it's done I'll be posting here the video :-)