If your old trans was rebuilt and you really want to save it it would be a lot easier to pop off the oil pan from the old engine and remove the connecting rods. My money is on a broken timing chain rail causing valve/piston interference on the old engine so removal of 4 conn rods from the bad side would allow engine rotation.

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2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

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1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k