Look in the DIY section; Members have driving a Torqx type bit into the Allen head hol and been able to turn the Bolt.

Then there is the already mentioned drilling.

I am assuming you can get some sort of Pry Bar or piece of Wood in ther to shift the Engine around so the Bolt and Hole line up.

It may be just lifting the Engine will allow the hole to line up.

Also the Arm can be un-bolted from the Block.

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84 300D, 82 Volvo 244Gl Diesel