Yes, the B60b and its cousin the BM60 were PRR-designed and built head-end cars used on the LI from the 1920s up til the end of express and mail service in the 1960s. Some went on to serve in MofW service.
The B60b was baggage/express, used most frequently in the later years for newspaper delivery to stations out east.
Numbers 715-724, 737, 738 are shown in the LIST-NRHS booklet from 1972 as active then. All were built in 1928 by the Pennsy.
718 was rebuilt to wreck train car W-56; 723 was said to be preserved somewhere but not shown where.
737 had a mail compartment (15', I think) added in the late 1940s and was reclassified to class BM60 (Baggage/Mail) and later rebuilt to wreck train car W-57.
738 had a mail compartment added in 1947 and reclassified BM60 #7738, then again reclassed back to B60 when the mail compartment was removed after the 1963 cessation of mail contracts. One of these two BM60 cars (7737 or 7738) is probably in the photo above. And, I believe one of these two cars is at the Oyster Bay museum now.
As part of the modernization program effected by the LI in the mid-1950s, these cars in the 700 series were given a new first digit of "7" when they went thru the shop. So, for example, car 737 came out as car 7737. Floors were redone, and the baggage doors which were wood (if I remember correctly) with rectangular window glazing were replaced with metal doors with round "porthole" glazing. They also got a small red and yellow modernization number decal on the right end of each carside to indicate the modernization.