A bad head gasket could allow compression to leak between cylinders resulting in low readings. From the picture, it looks like your head gasket is OK but hard to tell from just a picture. Stuck rings will also result in low readings. Take a small screwdriver and push on the rings through the exhaust ports and see if the rings have some “spring” to them. If the rings are not stuck they should push in slightly then spring back when you release pressure on them. Again, hard to tell from just the pictures but your pistons and cylinders all look OK except the one piston ring visible in the picture, that ring looks like it might be partially stuck in its land (in the portion visible through the top exhaust port).
Edit – yes, in your first pic it is normal for carbon to have built up in the exhaust area especially with the older oils used back in those days. That can easily be cleaned up.
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1957 Evinrude 3022
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20
1982 Evinrude 25hp
“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."
