The "trick" here is to NOT designate or claim the turf or grass strip as a
separate runway from the paved portion - if you do that you run afoul of
an obscure FAA airport dimensional requirement that mandates minimum
spacing between "parallel runways" (500' as I recall). Rather, you
position should be that it's all the same runway - except that one side of
it is not paved.

Yes, that's what we do at Nashua, NH (KASH). We operate some tail
draggers on the grass adjacent to the 5000 ft paved rwy. The tower
treats both as a single rwy for spacing purposes. I love it when they
clear me for the grass and tell me that it's at my own risk. Like,
landing on the pavement isn't either :-).

Tony V.