I just looked at the mounts I ordered and the package says 6cylinder! So angrily, I traced the part numbers back and online they are labeled under v8. They look roughly the same size as the old mounts.
Product number 8L-6038-B
The Parts CD omits much of the info about 52 flat-V8 motor mount parts but what I found was:
Bolt - 1/2"-20 x 3.40" long (note that '48 - '51 is a 7/16")
Upper insulator (rubber) - 8L-6038-B
It does say that for '52, 6-cyl and all V8's use the same parts. Seems like you're good!