As stated, the higher dwell reading is a closing of the point gap which advances the
You will notice a felt oil res. on the dist. shaft when you remove the rotor. These
sometimes never get oiled as they are hidden and the results is wear and slop on the shaft. This shaft is the lobe and advance plate and wear affects the dwell and timing to the point where the points are too close and can cause your backfire. Look for drifting dwell and erratic timing with a light on the timing marks.
i have had excellent results with point conversion kits for these older ignition systems. Mechanical switching has many wear drawbacks and is easily replaced with improved performing electronic ign. for short $$$.