I can't confirm what the TW is, but as you found the 2240RPM=60 is pretty common among Japanese bikes. I'd doubt the TW is an exception. The stock speedo isn't particularly accurate anyway, with the stock front tire it has the typical "optimism" of about 8%. So 60 indicated is more like 55 actual.
If you want something smaller, you can get loads of small digital speedometers that just use a magnet and wheel sensor, which can be calibrated to any wheel/tire size since it just counts RPM and then multiplies by wheel circumference you program in to get speed. Trail Tech is a popular brand and has a few different options, but if you want something small/discrete a bicycle speedometer works just as well.