PC: 75' piggyback flatcars on PC

[Jerry Jordak <jer@xxxxxxxxxxxxx>]

I have a question for the PC piggyback experts:

PRR in the mid-1950s bought and used 75' F39 class flatcars that could 
carry two 32' trailers. These cars were later transfered to Trailer 
Train and carried TTX reporting marks.

In the 1960s, the 40' trailer started to become common, and Trailer 
Train started to buy the more common 85' flatcar to carry pairs of 40' 
trailers.

What I'd like to know is: how long were the 75' flatcars in service, and 
did they make it into Penn Central in piggyback service?

And yes, I have several of these cars (the old Walthers kits) whose 
existence I'm trying to better justify on my layout. :)

Thanks,
-JWJ