your current gauge cluster will not work, it is a communicating type..it has a datalink to the ECM. you'll need to wire everything up from the ground on a new setup.
a mchanical engine will have the spots for gauge senders for the ones you need.. on the flywheel housing is a place for an RPM sensor.. I believe the flywheel is 132 teeth on the NGD.
temp, oil pressure the engine has sending unit holes already you can install your own gauges there. volts is easy. fuel just install a new sender and gauge.
your transmission is designed to operate on a J1939 datalink. you;ll need a mechanical to J1939 throttle box to operate it.. and it will work O-K. (the electronic engines run the electronic transmissions best but they will work with just throttle.)..
CAC sells such a device.
speed, your transmission has a single wire pulse sender for your speedo.. I believe its 16 pulses per rev. (they are either 16 or 40 depending on the vocation).
your electric fan will have to have a **LOT** of CFM to begin to cool that engine.. the other issue is if I remember right the RE300 pushes the fan out outthe back... most electric fans with enough CFM are designed to be puller fans and you need a pusher..
the DT466E was based off of the mechanical design of the NGD.. you may find that many of your belt-on accessories are the same.. there are differences between the RE and FE/CE versions when it comes to the fan and such.. do some studying but parts may move over so you may be able to keep your existing fan clutch setup on your new engine.
being an RE, throttle will be your biggest thing... you'll have a mechanical throttle all the way from the front of your bus to the rear.. I dont know how IH did it.. a lot of city and coach busses back in the day used an air throttle setup.. the throttle pedal is an air valve that actuates a mechanical linkage to your P-pump at the rear of the bus.. thus no linkages and extra long cables to deal with.. I dont know if there are retrofit air throttle kits or not or if its something youd have to build.. others with RE busses can comment on how their throttles are set up.. my work with vntage bus rescues of old busses have found everything from sticky bell crank setups to air throttles... but ive never retrofit anything like that.
there are electric setups too.. i just googled this as an example.
https://www.amazon.com/Trombetta-Thr...fdff1511c4d5da