Haraka ...
WK518 certainly had the 5 Point Seat Harness in 1977, which had the Seat QRB attached to the 5th strap that came up between the legs. The seat straps were/remain black in colour (I also remember the 4 Point Seat Harness where the straps were blue in colour). The parachute strap lugs that I remember weren't angled back then.
The straps visible in the above pic are almost certainly Parachute Straps with a revised design of lug.
This pic of Prince William in WK518 helps a little to identify the various bits of webbing
I'll have a look to see if I can find a pic of the parachute lug we might be more familiar with
Best ...
Coff.