Thanks again, Rob. I did actually look up the date of the engine, but forgot to mention it. The man who sold me the tractor also sold me two other model 23 Briggs engines. One of these engines may have red paint under the orange paint, and may have been on the Page tractor at one time. I'll take a closer look at these two engines and post what I find here tomorrow. Here are the tags on the other two engines.
Both of these other 2 engines were manufactured in 1960. Based on the way your tractor is configured, my bet is the 1964 engine currently in it is most likely the original.
I believe you have a 1964 manufacturd Red E model P15 tractor.