Assuming a 5" threaded collar I usually put the welded on ring 6" down from the top of the strut tube - that's for 10" springs in the 300 lb. in. range. You only lost about 2" from the removal of the 280Z insulator. The camber plate puts the upper spring perch about 1" down from the top of the strut tower.
If the fabricator shortened the 280Z rear strut tube to about the numbers listed for the 240Z strut tube in the Sectioning FAQ then he removed 3" of tube length. The inside length of the rear 280Z strut tube is 18". I suggest you remove 1" from the 280Z rear strut tube and add an appropriate length spacer under the shock.
Agreed. Looks like a basic stock bottom end with 1mm oversize pistons. Nothing special and with the damage shown I would probably just toss it and find another bottom end to build from.
Very common problem. You probably overheated the pads and/or fluid. There is air in the lines, you just need to bleed a lot more. And read up in the Brakes FAQ before spending any more money on brake parts. I can't think of a situation where you would need a 1" MC on any of these cars.
Is this installed on a 240Z or a 280Z? If its on a 280Z, then the rear strut tube lengths listed in the Strut Sectioning FAQ doesn't apply. The 280Z strut tubes are longer and the strut tower mounting point in the 280Z body is higher up in the chassis. For the 280Z rear struts you just cut out the same amount that's cut out of the front tubes.
Also, you lost 2" in ride height just by swapping out the 280Z insulator with the GC camber plate.
Won't be a sealing issue if you use any kind of silicone sealer. That type of casting porosity is common with those aftermarket covers. You can source the fill plugs locally. And the return policy is normal for products here in the USA.
The rear strut is cut too short. If the rear struts are cut to the correct length there should be a spacer underneath the shock 1 3/4" to 2" long (IIRC). If there is no spacer then your guy cut the strut tube too short.
Firing order is 1-5-3-6-2-4 and number 1 is between 7 and 8 o'clock on the cap. Wires are ordered counter-clockwise from there. That is the proper orientation. If your distributor is (was) not installed correctly the proper orientation may not work.
Either swap the shoulder harnesses for the correct bar mount or properly weld two tabs to the harness bar and bolt the shoulder harnesses to that. Get this wrong and you die.