The Sears 3.7 is usually a Poulan 3700. Old school magnesium cased saws. There is also a Roper based 3.7 sold by Sears from about the same time period, but there are far fewer of those, at least around my area.
The Sears 3.7/Poulan 3700 uses a 70 dl 3/8" 0.050 chain on their 20" bar. The Poulan 3400 and 4000 from the same time period also use this bar and chain.
In my opinion, these saws are comparable in quality to professional level Stihl, Husky or other top brand saws and can often be had for $100-$150 for a 56-61cc saw.
The fact that there are many, many of them that still run great 35 years after they were manufactured (they were built in the 1980s) is testament to their quality construction.
I heat my house with firewood and cut most of my wood with one.
Edit: I see beavis331 posted in a similar vein while I was writing my post.