Your NG pressure in your house will vary according to what area you live in. Here in this town the gas in the street is measured in pounds or PSI, the regulator outside your house drops it to perhaps 9 inches WC, the one in your appliance like your water heater or stove drops it to 3.5 inches of water column. Your orifices are drilled out to deliver X number of Btu's at a certain pressure usually 3.5 inches WC/
Since the 9-10 inches of WC is close to the regulated propane pressure and your mileage may vary straight connection might work.
Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10