I'm no expert but I've found an excellent reference page (Honda 750 buyers guide) and here's what he says
K0-K1 Fork Covers
Painted same color as gas tank and side covers.
On bottom-half of vertical portion are threads for a small reflector.
On horizontal portion, one hole at its end for a turn
signal stalk to go through and then into headlight shell.
K2 Fork Covers
Chrome.
On bottom-half of vertical portion are threads for a large reflector.
On horizontal portion, one hole is at its end for a turn
signal stalk to go through and then into headlight shell.
Looks like K0-K1 shape, but in chrome and with bigger reflector.
K3-K6 Fork Covers
Chrome.
On bottom-half of vertical portion are threads for a large reflector.
On horizontal portion, one hole is at its end for a headlight shell bolt,
and one hole inward of that for a turn signal mount.
Left fork cover has a square mounting hole for turn signal buzzer.