Yes, I'm pretty sure the 77 column has a splined bottom end of the column shaft. So, the 77 intermediate shaft has a splined clamp to fit it. The 79 shaft end is a slip together deal with a hole that you put a bolt or pin through the hole and tighten with a nut. So, you need the 79 intermediate shaft.
For the switch, whether you need the switch or the lock cylinder, you'd need the 79 parts.
Since the headlight dimmer switch is on the 79 column, you could connect your 77 floor switch wires to the wires on the column and use the column dimmer.