NO! LIRR leased Pennsy locomotives of classes K4s, E6s, H9s, H-10s, and G5s. Several L1s Mikados were on the property at one time as well. NONE WERE LETTERED FOR THE LIRR. However G5s and H-10s locomotives may have swapped tenders with LIRR locomotives being serviced at Morris Park. I have never seen a photo of an E6s with an LIRR tender.
It is interesting to note, of the locomotives permanently enshrined at RMPA, the K4s, E6s, G5s, and H-10s, were all leased to the Long Island at one time or another.
If you are a Long Island fan and not a member of the PRR T&HS, you are walking in the dark with blinders. Great resource and font of information.