All metal, painted..looks like all the 70's ones, cept it has brakelite switch built in..like 78 did, and the fluid pot is taller..
I have a 78 750 K MC, looks same but not as tall.
I have not noticed the brake lite switch on earlier ones, not sure if that is first year?
Also this was on a 77 f 750 brakeset. I do not actually know for sure what the 77/78 f's used for a MC.. it may be OEM...