OUr '07 Allegro Bus came equipped the same way as your Newmar. We had HydroHot but it was the model without the engine preheat feature. It was plumbed up with the Motoraide feature which allowed the engine to supply heat to the boiler when driving so the heater hoses were in place. I contacted AquaHot and had them send me the parts required to add the engine preheat feature to my unit. They sent me the pump, the switch, and some connecting hoses. Details of my installation can be found at RVcruzer.com - Installing the HydroHot Engine Preheat System
. All wiring harnesses include wiring for the engine preheat switch so you don't have to run any wiring. Just plug the switch into the existing connectors. If I recall, the parts ran around $300 for everything.
I have found that the AquaHot preheat system does a better and faster job than the 120 VAC block heater. The block heater gives you the temperature reading on the gauge before starting but once the engine is running the temp drops a bit because the block heater only heats a localized spot in the water jacket. The AquaHot uses a circulation pump to circulate the coolant. The overall temperature is the same as the block heater but the warm water is spread over a larger area so the engine retains more of that heat. It's also much faster to build up heat than the block heater. For boondocking or last minute warmup decision the AquaHot preheater is hard to beat.