If you really wanted to use the TH400 transmission your best bet would be to find a "core" 4wd 400 transmission with the proper transfer case attached. This would give you an economical output shaft & tailhousing. Then you would have to dismantle the P30 transmission just about down to the case and install the "core" supplied shaft & tailhousing. Then you will still need to figure out what you are going to do for the crossmember, drive shafts, and shifters. I think the 727/205 from behind a 6BT could be a bit easier and possibly cheaper. Check your local prices before you you make your final decision.