I run the newtronics on my cb450. The 350 would be the same. Counter clockwise from the "T" and "F" or "LT" and 'LF" marks are a pair of un-lettered lines/marks about 4-5mm apart. These are the full advance marks. Hook up the timing light to the left cylinder and make sure you use something to shield the rotor and pick-ups from the flashing timing light. Since the newtronics use an interupted beam of light to trigger the spark the flashes from the timing light can throw off the timing. Start the motor and increase RPMs to at least 3500-4000. Point timing light at the mark and rotate the pick-up plate until the marks are lined up. Use the mark to the left for maximim advance or try to split the marks.
Switch cylinders and repeat. If it is not the same you have to loosen the screws holding the right pick-up and move it to obtain the same mark alignment.
As a side note, I have found many Honda twin advance units that have way too much advance. So when you time static the spark advances too much and if you time dynamic (with the light), at idle it is way too retarded and you cannot get a regular idle. (either too fast or none). This is a real common problem an all old Honda twins and if you know everything else is OK (compression, carburation etc.) it is most likely tnis. To fix this you need to equally bend the tabs on the advance unit that stops/limits the advance weights travel. The rest is trial and error unless you are clever enough to do this on a bench with a protractor, it is possible.
Hope this helps.