Hello John,
These 6 cylinder W107 cars were quite popular in the rest of the world. In the USA they are scarce since they were not offered here.
A lot of W107 enthusiasts prefer the lighter and more limber six cylinder 280SL to the heavy and sluggish emission laiden 450SL of the era.
Since no W107 280SLs were offered in the US new, examples which made it here afterward are "euro spec." mostly. This means a lot more power, lighter and better fuel economy. If your lucky these cars may still have the pretty small chrome bumpers instead of the massive USA safety bumpers.
A typical W107 280SL may have many desirable features; no or less emisssion devices, high compression engine (more power), small original chrome bumpers, stick shift, euro headligts (better lighting).
On the other side of the coin, they often show up with; roll up windows, non leather interiors, and no AC. Although the M110 six cylinder engine in these is lighter than the V-8 in the 450SL, it is still heavy and complicated with its dual overhead cam arrangement.