The PM 6 is not so bad to work on, just different from the way most saws are put together with the fuel line/nipple in the tank that butts up to the fitting in the carburetor. The PM6 is a great top handle saw for trimming and such, not the first choice for bucking larger stuff. I think they are easier to work on than the 300 Series saws but then again I don't mind working on the 300 saw either. If in fact it is a Mini Mac 6 then it has little value unless you are an extremely patient man. A running Mini Mac is handy for trimming but not a lot beyond that.
The PM55 is a nice little saw and as noted, plenty of parts availability if you need something. I have a 16" bar on mine and really like to way it runs and cuts.
$100 for both is a good deal if they are clean, have good compression, and no broken parts as long as you are handy with whatever repairs may be needed.
Mark