Engine Identification!

are you sure the first mark is an I? could it be a mis stamped T?

on early 60's mopar's the first letter was the year, they did not use I, but did use T and T is 1963

225 is displacement
R regular gas
1203 is day and month,, March 3rd
E is also odd, as E indicates a cast crank,, cast cranks came into use in the mid 70's,, so something does not match up there either

at least you don'y have the x or maltese, those indicate undersize cranks...

I also recommend postion your question over at slantsix.org