I'm not sure an '85 transmission is compatible with an '84 car, you may be opening up a can of worms there. Last year of the 123 had a different transmission, different torque converter, and different rear end ratio.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC