I suggest at least one 1 foot square Sheet of 3/4" thick plywood against the Pan to spread the load over a larger surface area (or glue together 2; 1/2" thick pieces) and then the 2x4.

Also take a look at the gap between the top of the Bell Housing and the bottom of the Fire Wall. When that gap closes and the Bell Housing hits the Fire Wall you start lifting the whole Car from the Oil Pan.

On Mine the Previous owner did that and dented the Pan.

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84 300D, 82 Volvo 244Gl Diesel