have you checked Hunley sales ans service !they have been doing it for a long time and are located close too Cummins ! IF intrested contact my e-mail and i'll get you a phone n.. they repower any brand !
I had a 8850 Kinze repowered with 450hp for about six years and had only one major problem with the rear main seal going out but it was covered by the cummins warranty. Other then that I think it was worth the money. I have traded it off for a 9400T last spring and the resale value was very good and the farmer who owns it now has had no major problems with it.