I have seen the Tacho read incorrectly before, it was a US kit builder with a 360R. That was solved by correcting the dip switches on the Tacho. In that case the Tacho was under reading. OBD is present on on some models, EU spec cars and UK SuperSport 1600 example, but I haven't seen it on 420R. Your speedo flicker will depend on the age, either pre 2016 where the sensor is a little unreliable, or post 2016 where the sensor needs to run closer to the trigger wheel than the previous version. Both sound simple DIY fixes, but if Team Leo's is near maybe drop it into them for assistance.