Join Date: Feb 2011
Location: PNW Canada
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IMO you really have 2 ways to go about it....
1) SM465 or NV4500 (both GM trans) mated to the cummins using the adapter the factory 4BT bread vans used. Without overdrive (SM465), you most likely need to re-gear the axle (14boltFF) to 3.21 for highway speeds.
2) Use a 5/6 speed that comes with the cummins. With overdrive you may be able to tolerate a 4.10 axle. 3.42 or 3.73 would be better.
A body lift can be helpful in positioning the engine. There is also an oil pan difference between 89-93 and 94+. The 94+ style should let you place the engine slightly further forward; although not sure if that's beneficial or not.
93 W250 Club 6BTA |5spd |60/80/3.54/Lockright |4" lift |315/75R16 |HX35 |5x.012s |BD pin & gov spring
90 D250 6BT |5spd |D60/3.54/Lockright