I found figures for a 1.6 litre Sephia that said 105 HP @ 6200 RPM. No mention of red-line, but 6500 would be normal. 6000 RPM is usual max for this sort of engine; 5000 RPM if you expect an older engine to hang together.
Remember that after-market tachos may need calibrating. Check against expected RPM calculated from road speed, gearing and tyre size.
Here's the details:
100km/h is equivalent to 1667 metres/minute.
If driven wheel has effective circumference of 2 metres, it's doing 1667/2 = 833 RPM @ 100 km/h.
Typical final drive is 3.5 to 1 and if 6th gear is 0.75, engine = 833 x 3.5 x 0.75 = 2200 RPM.
Measure wheel working circumference by applying a dab of tyre black and rolling along smooth driveway. Calibrate speedo by stop-watch or GPS and you can then derive a tacho calibration by driving at (actual) 100 km/h in each gear. Simple.
No worries. This is the simplest and most effective way to calibrate the tacho. Another method is to use a pulse generator, but that's not always convenient for a tacho that's already installed.
Another method is to use a stroboscope on some moving part of the engine. You can even use the AC flicker from fluorescent lights. The AC, BTW, is a very accurate 50 Hz (60 Hz in some countries); it's good enough to run the clocks by.
You can add a circular card with black/white sectors if you can find a suitable spot on the engine to try the above.
P.S. Tried it last night with fluoro on the top of the lawn mower. You definitely need a card to see the effect; too fuzzy otherwise. BTW, Briggs & Stratton only manages 3000 RPM easily; performance gear and stronger valve springs might get me 6000 RPM; Watch out grass!