John,
Your slide, barrel, and frame are all "two piece". Guns like yours are most often referred to as "cut and weld" Combat Masters. (Because that's how they were made back then). Your description would indicate that it was likely never returned to the factory for the slide replacement that was offered in those days. I'm sorry to be the bearer of bad news, but because of the angled slide serrations you've described, you likely have a slide with limited life. As such, you should carry it much, but shoot it very little. There's no warranty left on those older pieces. (The Seattle firm went bankrupt in the late 80's). I've heard that when the Detonics USA shop was in Georgia, they fitted new top ends on such guns, but not for free. Also, the new top ends were stainless, since Detonics USA didn't make any blued steel guns.

Your serial number would indicate that your gun was shipped around 1977 or 78. If it's a good working piece, it's value may be about $400 to $450.

Hope this helps,
...Deeton