There is no longer a Rule 150. However, there is a Rule 5 and it makes clear that DL no longer arranges or pays for this service. If you do choose a LGA-JFK connection, make sure to allow a lot of time to account for the vagaries of baggage service and traffic at LGA.
RULE 5: INTER-AIRPORT TRANSPORTATION When a metropolitan area is served by more than one airport and the passenger requires connecting service with arrival at one airport and departure from another airport, transportation between those airports must be arranged by and at the expense of the passenger. Baggage must be claimed and rechecked by the passenger.