The problem with these kinds of conversions is getting them legal. Having been through the entire process with my OM617 into 380SL I learned a bunch.
380SL Diesel Conversion Project
In California there are 4 criteria.
1) the engine must be from the same or later donor vehicle as the target
2) the engine must be from the same "class" of vehicle (passenger car, light truck, heavy duty truck)
3) all the smog equipment must be present and operational (confirmed by a state inspector)
4) vehicles '75 and earlier are exempt
In addition no non-vehicle engines (i.e. stationary power, industrial, etc.) are allowed.
The only way to use a Kubota would be to do a legal conversion first and get the vehicle re-titled as a diesel then re-do the swap with the non-eligible engine. This would work because diesels are not inspected if they are '99 or earlier.
This is for California only - every state is different. And strangely enough CA is one of the more lenient states for swaps.
Just for the record i'm getting a consistent 29.5mpg for regular driving and this is my daily driver.