I have since figured out its a 361 for sure. No its not original. the previous owner had it and then bought a school bus from a dalles Oregon (I thin vehicle auction. The district policy was they had to rebuild engines before selling to public. he took the engine and NP540 direct trans out and put it in the d300 in place of the original poly.
Soo much torque. I hauled 4600 lbs of gravel on the highway last week then up into the back hills and I could still start out in 3rd gear on the flats. :/) couldnt even tell it was loaded.