For anyone who was dying of curiosity to know, in no particular order, and with uncertainty that this list is complete, here are the 9464 Standard O boxcars that were produced with a die cast frame. Some of the blurbs on the Lionel website indicate that some of the PS1 boxcars were produced with die cast frames. As an aside, Lionel also has a series of 6565 (6464 sized) boxcars with die cast frames.
B&M 6-17285
PH&D 6-17234
C&O 6-17268
WP 6-17233
CoG 6-17224
MR 6-17226
PRR 6-17220
NP 6-29259
NY Central 6-17247; released for separate sale, and, as part of the 6-17246 NY Central Freight set, which included 2 additional NY Central Std. O Boxcars in the Pacemaker scheme, both with die cast frames, 6-17248 & 6-17249, and a Pacemaker Caboose, with a plastic frame.
D&H 6-17258
Rutland Reefer 6-19552
KATY 6-17259
CP Rail silver 6-17260
CP Rail green 6-17261
CP Rail red 6-17262
B&O 6-17270
SRR 6-29257
WM 6-17269
UP 6-17250
NP 6-17243
NP reefer 6-17316
ACL 6-17257
BAR 6-52566