A little advice please

Hello everyone I recently got a free 68 Galaxie 500 XL Fastback given to me by my inlaws. I know this is a Mopar forum but hear me out. The car currently has a 427 in it and I want to put in a 5.9 24Valve Cummins in it instead. I know I will need the motor mounts, engine wiring harness, computer, tranmisiion and all the trans components, so my question is what else will need to be done? Also can anyone give any input on how to make the speedo work and other sensors work with an original gauge cluster or will I have to build a custom cluster? I welcome any and all input, opinions, advice, etc on this subject.