3951207 cartridge unit-stereo tape player 8 track

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Part number 3951207 shipped in a box with PC8S-536 stamped on the side. Clamshell style package RCA cartridge, Music of the USA Vol. II starring Lorne Greene. Assembly manual page 15 C2 Miscellaneous Shipping List for RPO U57. Made in 68 and provided only for the 69 model year.
Pictured, original package and an open example of the 8 track itself.