Denny -
Thanks for the catch. I'm trying to write my recap as accurately as possible for anyone who finds it when searching for info on mounts.
I was wrong about the "hardened" 3/8-inch end bolts in the front mount. I interpreted the MPC 3/8 "carr hd" to mean carrage hardened. It means carriage head. I should have read the
meanings of abbreviations in the MPC before I posted my recap. I edited it to correct the error.
Regarding the drilled 3/8" bolts. I'm still not convinced that my '54 were drilled. It's no big thing either way. Darryl and I both looked at them to see if they were drilled. We didn't see a hole. I believe that they are original to the truck, but who knows. The '54 Shop Manual describes the nuts for the 3/8" bolts as "self-locking."
EDIT: Well, I just checked the '48-'51 Shop Manual. It also says that the 3/8 nuts are "self-locking". The MPC describes the nut for those years as "sltd" (slotted). I assume for a cotter pin. Bottom line - I dunno! All I know is that the 3/8" bolts in my mount were not drilled.
I'm glad that you forced me to dig a little deeper.