Those digital meters can be confusing and misleading, especially if you don’t have them set correctly. When you say “no reading”, I am assuming you mean infinite ohms or an open circuit. I am assuming that the green wire is the coil primary lead and the black wire is the coil ground, common to the primary and secondary leads. The proper way to test the secondary circuit is to touch one lead to the coil ground lead, the other lead to the plug terminal, this should show several thousand ohms. Touching one lead to the coil ground lead, the other lead to the coil primary should show about 1 ohm. Needless to say, your meter must be set properly or you will misinterpret the results. You may want to try testing the other coil first and compare the results before buying a new coil. Keep in mind, that even a coil that reads correctly on an ohm meter may be defective, especially if the secondary has an external leak/crack allowing arcing to ground.

1- touching your probes together will give you your 0 ohms referrence (max conductivity since the probes are touching themselves. IF using a needle meter touch the probes and …adjust the needle to 0 ohms to establish a referrence of 0 ohms on the scale being used .Always reset the needle to 0 when changing to a diff. scale.

Make certain the meter’s inside battery is fresh……..(they all have a battery inside) !!!!

2- that said probing the green and black will give you your primary winding resistance 1-3 ohms max not much more (if using a needle meter use 100 ohms scale or lowest possible scale above the expected 3 ohms reading

3- that said ….. black to HV pin probing gives you the secondary winding at 4-7 kohms … if using a needle meter set the scale to 10 kohms !!

if your digital meter shows nothing (no value) similar to when the probes did not touch themselves before starting step 1 above …. you have infinity … open …. infinite resistance (air) which is an open secondary winding

https://www.electronics-notes.com/articles/test-methods/meters/multimeter-resistance-measurement.php

I am assuming you were checking the primary circuit during you restest, correct? .8ohms seems correct, zero ohms means the primary is completely shorted….That being said, those digital meters are very hard to read, and not all that accurate when reading super low resistance readings (below one ohm). The readings seem to jump around and add to confusion. I admit to being “old school”, and love my simple Stevens AT 101 analog meter….Like anything else, I’m sure there are some digital meters that do a great job in the low ohm range, but the jumpy readings sure can be confusing….
OK, so you have ordered a new coil. If the new coil doesn’t solve the problem, then I would swap the points to see if the problem swaps cylinders….If not, I would swap the condensers. Bad condesners are often overlooked, and they do deteriorate with age. And, just because they are new, doesn’t mean they are good. I am trying to remember if you replaced the points and condensers, am assuming you did…If so, did you use an OMC ignition kit?

You did right in lightly greasing the mag plate. Low voltage does not cross that junction, only high (spark) voltage which has no problem getting past the thin smear of grease.

Pressing down on the mag plate changes the breaker point gap and clearance between the coils and magnets. This could be significant if it is worn really sloppy. However, they all have some wiggle.