Most likely it is jammed in the relieve position and the valve has been adjusted to get closure. Looks like the operating cam can be installed upside down.

I can send you the full size scan and you can see all of the parts. The forum limits the size of the uploaded image to 293K which is barely readable...

It is not that straight forward of a removal process. You have to drive the locating pins into the engine far enough to rock it out from the top but without driving them all the way through as they will then be in the pan with the oil. The valve rocker has to be backed off and the push rod removed. Also the decompression linkage.

Sometimes the cams on the compression release get worn. Had one like this on a d4 4g.built them up with a little braze 20 years ago seam to be still working.

The cam levers are keyed to the cam shafts....not likely they would get reversed. Worn cams would be the most likely cause of the compression release feature not working. If linkage is disconnected make sure the levers are in the correct position. Forward for start, back for run.