[Knorm65]

UMM not trying to be snarky here But can you explain a little better the 2 by 4 screwed to the bottom?
And since I'm asking why was the brake rod rail cut and removed?

The 2x4 is not on the approved install guide for the GM AC, but the brake rod support being cut is required for GM AC install.

 

[Knorm65]

The GT was not designed for a/c. That is for GM compressor, which is a long cylinder shape. An R6, I think. There was no where else to fit it in the engine bay. The other system, the ARA, used a compressor more like the square Ford York or Tecumseh and it was small enough to mount over next to the thermostat housing.
Other signs of a GM compressor are the alternate locations for the coil and washer bottle.
With the condenser in place in front of the radiator, I am inclined to believe, but am probably wrong, that they used a smaller battery to fit down in there.
Has anyone seen evidence of a rotated battery/tray that keeps the battery away from the condensor?

The GM A6 compressor AC installation generally includes a trap door cut into the belly pan along with a new battery box mounted in the center of the belly pan 90° from the original.

I opted to use a 6”x6” AGM battery instead of the horrors the dealership mechanics inflicted on the cars originally.

Also that little black box on top of the pedal board is a vacuum switch for the compressor. Pretty nifty little guy. Whenever vacuum is 0 it disengages the compressor clutch. So it automatically shuts off at idle (ported vacuum) and at WOT.

 

[Knorm65]

The GT/J gas cap makes a good oil cap too. I’ve used it for a few months before I decided I liked it on the gas tank better.

You can also use a 1970s Chevy C10 fuel cap for oil and fuel on an Opel in a pinch.

I think I’ve found this one on every Opel I’ve ever purchased. Vented Gas Cap Polished Stainless Steel Chevrolet C10 1960-1971

 

[Knorm65]

It is late evening, but have to ask. OEM Opel oil filler cap would be non-vented.
Vented oil filler or gas cap will function as a breather vent?

It probably acts as an oil leak on an Opel lol.

I’m not sure the ones I can across were vented. You could probably plug the vent though.