Yes it was indeed the last year Ford made them. Believe it or not the Ford flathead continued in production for MANY years -- in FRANCE. They used them as tank engines till probably the late 70's. In fact among the hot rod fraternity there was recently a LOT of excitement about a large amount of NEW bare blocks being released by a surplus outfit. All the standard Ford parts fit them & they were being grabbed up as fast as they could be shipped.
http://www.jalopyjournal.com/ Do a search for French flathead if you would like to read about them.
I don't remember exactly what the CID of the 53 was , but I ran many
"3/8's X 3/8's" flat heads ( 296 CID) over the years. Had a few set up with ARDUN heads too ( Wish I had a set now!!)The biggest flathead I ever heard about was one built by some guy in Oregon--- He got one up to 354 CID!!! Mostly with a billet stroker crank -- I remember seeing pics of it -- the pan rails were ground out to about 1/8 inch wide to clear the crank!