Bought some Yaiba rb6 bits. Slightly lighter than the K bits - the wide front rear holder is 3.1g, K part is 4.5g.
Front Yaiba is 4.4g, motormount is 16.7g, steering arms are 4.2g (no bearings), plate is 2.4g.
Not sure about the other K part weights. Have Exotek steering atm, will pull that off some time and compare.