Apparently the M46 had only these ratios:
Gear ratios: (1) 4.03:1 (2) 2.16:1 (3) 1.37:1 (4) 1.00:1 (5) 0.79:1
Source:
http://www.nuceng.ca/bill/volvo/database/tranny.htm
Note that the OD is a relatively high (numerically low) ratio.
I do know the M46 did get different OD pressure relief valve shim/spring packs for higher PSI for higher torque engines (D24T included).
What tires are you running?