From RCT&HS MP&RE Facebook page today:

SEPTA attempted to donate the car to several different organizations, but a state law requiring it be donated to a municipality scuttled those attempts (PCBs scared off some rather cautious local governments).

Hooray! One of the original Pioneer III design high-speed MU cars was saved.

Pioneer I is a stainless steel airplane currently displayed by the Franklin Institute in front of their building. Pioneer II is the Burlington Zephyr 9900.

The design began as a single coach with HEP and A/C with 88 seats and weighing 53,000 lbs. Budd built one car as a demonstrater in 1956. In 1958, PRR bought 6 MU cars to the Pioneer III design and they specialized in Phila-Harrisburg service.

In 1963, the City of Philadelphia (there was no SEPTA yet) bought 55 MU cars with higher speed and named them Silverliners. 38 went to PRR and 17 to Reading. Some of PRR's MP54's were worn out and RDG's old cars were OK but traffic was up and they needed more cars.

The cars ran for 49 years under RDG, CR and SEPTA.

9001 was set aside for preservation but no eligible Museum wanted a car that had a PCB transformer. RDG 801, preserved at RRMPA, has an air blast transformer, Finally, SEPTA sold it and RCT&HS was high bid.
c
Phil Mulligan

Note: the name "Silverliner," was first applied to these RR MU cars. Whether it was based on the CNS&M rebuilt interurban cars is an interesting question. I think it was. When the huge fleet of GE MU cars (still running) arrived, Marketing named the Pioneer III cars Silverliner I. these cars Silverliner II, St. Louis cars Silverliner III and the GE's Silverliner IV. A later group of Hyundae-Rotem cars are Silverliner V.