I would start by looking for tag on housing. Evens, Tempco is popular one , other name I cant remember , you may find a parts blowup on unit. Finding exact instructions on your make, year and model is highly unlikely. Reaching up and getting some pics and vids you can start a plan of attack.
Sorry to say, the title of thread doesn't even mention heater core.
95 Monaco Crown Royale
M11 400hp, 4060 trans.
Aquahot, Generac Guardian7.5k