yep the bottom cover bolts onto the indicator switch boss. Sometimes you may find also the lower part of the cover flaps araound too. I used electrical tape wrapped around the column to build the diameter of the column up a bit. I'm assuming you are using a standard 1600 indicator setup and covers?
ah righto. all makes sense now. i'm still trying to find a decent (or new) combination switch to suit a 38mm column. the elec plugs on mine are smashed, and for some reason the previous owner painted it. not gonna work so well.
i bought a 1600 JDM cover from craig (tokyo 2u), the one with hazard and separate park lights.