If the cars are Amtrak certified for NY Penn,they should be Ok to Willets Point Station,
However LIRR over the years since the Worlds Fair,allowed most of that station turn moldy in place,
and use it as a base for equipment experments.
That changed after the US OPEN tennis facilty and Citi Field were built,requiring a upgrade of the current Port Wash
Mainline hi-level platforms,one of the other plaforms is upgraded to allow "heavy interior cleaning" of M-3's and M-7's
until Amtrak replaces the Running repair shop at West Side Yard(Removed for the Tunnel Box build)
Since the DE's and DM's have a some what LIMITED HEP capy and the oddball 36 point combo MU/DoorComm setup,
why not use an Amtrak P32 DM(or 1 of Geeps with HEP) with an Amtrak crew and LIRR pilot crew for the trip
to/from Sunnyside/Willets Point.
Or is there "friction" between Amtrak and LIRR that makes it impossible?