I have a 70 250 that recently has shown signs of what I have taken for ignition break down (coughing, missing in light to moderate acceleration & disappearing in moderate to hard acceleration) Now it has progressed to where it hardly runs ( major coughing & backfiring possibly thru carbs). Thank-you to M.B. Doc for the spark plug update. The compression test for cyl.1-4 were 175-180 lbs. with spark plugs showing light-medium brown deposits, cyl. 5&6 were up @185lbs. (possible slight carboning up) with the plugs wet & blackish. I have replaced the plugs, cap, wires, coil & points (rotor was B/O). It still runs like brick out house. points gapped @ .012", plugs gapped @ .020" My ignition utilizes a coil w/ neg. terminal going to ground, 2 resistors, a transistorized ignition control box and a distributor w/ points. I believe it to be a version 1 type transistorized ignition.
Can anyone tell me how to test the ignition control box or any other tests to cure this problem I'm having?
I have been thinking of putting in an after-market electronic ignition w/photo-electric pick-up to eliminate the points, can anyone advise me (pro or con) on this idea?

First of all the point gad is too close. .016-.017 it the correct setting.

I should have read the rest of your post but the plug gap is also wrong it should be .028" gap.