Gday EKSPCL
I can see three wiring loom holders,
one below the brake master cylinder, one up high, & one down lower
by the regulator.
The bracket under the heater hose hole, is for the original throttle return spring.
It can be removed if you run a cable accelerator.
So can the two screws below the heater hole, & the two screws below the brake master cylinder,
if you delete the original throttle linkage that runs across the firewall.
The regulator holes can be filled as you mentioned, if an alternater is fitted.
The wiring loom hole between the master cylinders can be filled if you
run the wires out of the cabin & under the front gaurds.
All the clip holes on the inner fenders can be filled along with the terminal strip holes.
Hand brake can be deleted from the engine bay if you use a side mounted HQ handle, or center mounted jap set-up.
I have done some of these to my engine bay in my FB.....
See here
Mine still uses a regulator, I just mounted it inside the cabin, upside down,
in the original nuts welded to the firewall, then smoothed the engine bay side.
Mine is also still fitted with the original throttle lingage.
Cheers
Jeff