Final drive and gear ratio for 82 diesel westy?

[captainpartytime]

I'm thoroughly cornfused now...my tranny code is DK 21 05 2. According to my Bentley that means it was manufactured on May 21st 1982. Now, when I cross reference the tranny code letters to the brickyard site http://www.brick-yard.co.uk/VehicleSpecific/T3/info/gbx.htm it confirms what I thought that DK trannys were from aircooled vans. This is the original tranny from my diesel. Any ideas? I'm basically trying to figure out (using Myke_W's calculator from dubdoctor.com) what my turbo diesels RPMs will be at max torque and RPM's at max power with my bigger rims (15") and tires (215/75/15). My baseline (70 HP @ 4500 RPM / 133 Nm @ 2600 RPM) is coming from this graphs numbers with stock tires (I'm assuming)