It's a Schwinn frame sold as Excelsior, so that's a Schwinn serial number. The paint looks great so I'll assume the serial number is easy to read and begins with J79 followed by 4 more numbers, all on the bottom bracket.
As stated above, the forward facing dropouts make it postwar. The serial number charts begin in 1948, before that were all lost in a fire. However, following the letters, I've estimated and backdated the serial numbers, and immediately after WW2, it looks like they started with "A" and each year progressed with the next letter. A=1945, B=1946, etc. Winding up with "H" in 1951, before they began stamping the dropout instead.
There shouldn't be a "J" with the dropouts facing forward that is stamped on the bottom bracket.
Sometimes, they switched to the next letter at the end of December, would make it a possibility that a "J" was made at the end of 1951. But yours, with a 79xxxx is too high a number unless they left off at a high number "J" before the war.
The cranks may have a date code on them. You'll have to pull them off to see the numbers.
I found an "I" number, which throws another wrench into the works. I'd like to solve this mystery. If yours has a date code, that would be a big help.