A few things.
1. Don't listen to the "a newer saw" is the way to go folks here. See if those "New" saws they have now will be alive, running and be able to get parts for in 50 yrs. My gut tells me nope. Plastic junk in my opinion. (I'd also like to see a "newer" plastic saw survive falling out of my tractor bucked several times.....hey, it happens)
2. The pics you attached look like it has a manual oiler for the bar. To my knowledge, all Super XL's had come with an auto oiler. So it looks like that saw could be a regular XL-12. The XL-12 came with 14, 16, 18, 20, 22 and even 24 inch bars. Without a serial # I can't say for sure, but based on the pics of your saw, type of muffler, style of handle, it looks like late 60's perhaps up to 1970 or 71. If the serial number has 7 digits, then it's a '63 up to maybe a '66. In 1971 or 72 the XL-12 changed to red from blue.
3. Your "heavy" saw comment I found kinda entertaining, since back in the 60's the XL-12 was marketed as "the lightest direct-drive chainsaw". XL supposedly meant eXtra Light, and the 12 was the weight of the saw head. (12 lbs)
4. My XL-12 with it's pretty new Oregon bar and chain would make yours look new. It's either a 1963 or 64. Has slight differences from yours.
A local guy that does mower/chainsaw repairs here asked the same thing when I needed a new chain (and I got a new bar as well) a couple years ago. "Are you sure you wanted to put money into that old saw?". I said, without a second of hesitation, yup. He shook his head. Did the work, tuned up the saw a bit (new plug, carb adjustments), and then tried it out for a few cuts behind his shop. He had a much different opinion of that saw when I picked it up. Pretty funny.
5. I need a saw, that does it's job reliably, and well. I've been using this saw consistently for the past 26 yrs.Prior to that, my dad used it to keep his two wood stoves going since it was new. If I had an endless supply of money, I'd have a new $1500 saw. But probably wouldn't be burning wood, come to think of it.
I'm sure that the day will come when I'll have to buy a new saw. But it'll be a sad day, and it'll feel like I've lost a member of the family. $400-$500 buys a lot a firewood. Even more when it's free