Sorry, Duwen, I missed your post with that block date code. I think you are correct with the 1958 interpretation (someone will correct us if we are wrong).
I248 = Sep 24 58
L248 = Dec 24 58
Nice photos of your truck that you linked-to on the other discussion board. Looks like you are very industrious. Pictures are nice to see - too bad none are allowed here.
It looks like you have a 54/55 235 valve cover (it has breathing slits in it).
Yes, the head date code is under the valve cover.
