Cornbread -
Your Mod. 27 dates from 1975-76. It's built on the "N" frame, which at the time was S&W's largest handgun frame, and is essentially the same gun that was developed to fire the then-new .357 Magnum cartridge in 1935. You didn't say when you bought it, but if relatively recently, and assuming it's in good condition, at $350 you stole it. They're currently selling, and selling pretty quickly, for about double that around here. There are basically two types of S&W revolver people: those that have a 27, and those that want one (mine dates from a couple years after yours).
The Mod. 10 was manufactured in 1974. It's built on the smaller (mid-size) "K" frame, and is derived from the basic .38 Special Military and Police model that Smith has been making since about the turn of the century (the last century, that is). It's a much more common gun, and also doesn't carry the cachet of the .357 Mag, so values are considerably lower than your Mod. 27. Depending on condition, $400 is pretty much the right price. IMHO, everyone should own at least one Model 10.
As you correctly noted, the serial number on S&W revolvers is the number on the bottom of the grip portion of the frame, known as the butt. Any other numbers or number/letter combinations you might see in the frame cutout are known as "assembly numbers," which are used to keep track of fitted parts during manufacture and have no particular significance. As you probably know, having the boxes, along with any original paperwork and tools, adds to the value of any gun, especially guns that are considered collectible, so be sure to keep all that.
Hope that helps, and thank you for your service.
ETA: Just noticed that you said you bought both guns this year - yeah, you definitely stole that 27!
sparkz: 1982