Nice Z and it looks like it is unmolested. Good find.
Agree...running hot would be either the fan clutch or the thremostat.
Fast idle means that too much air is going into the intake manifold.
In all the FI Z's that I have played with 76, 77, and 78 when you unscrew the oil cap or pull the dipstick, the idle should drop and the car should just about stall. If not, somethings wrong with the air side of the FI system.
RULE #1 Don't start taking things off the motor to simplify UNTIL you get it running right.
Check and listen for hissing air leaks, BCDD Valve (under the throttle body) stuck open, Air Bypass valve stuck open, missing or cracked vacuum hose (VERY COMMON) ANYWHERE in the whole car, fast idle servo for the A/C stuck.
Also, I don't think I see a vacuum bottle anywhere. There should be one somewhere. Check its hoses.