All good points, Joe! I missed the battery disconnect, which, unless it's the NASCAR approved 1,000 amp model, is worthless. ANY source of potential resistance in a starting circuit must be avoided like the plague- - - - -even 1/10 of an ohm is way too much to allow good current flow. The reason for measuring cranking voltage is simple- - -it gives you an indication of the current flow (or lack of it) during the "no crank" episode. Let's say you have an intermittent open or high resistance circuit on a hot start- - - -the battery terminal voltage during the "grunt" will still be fairly high, 11 volts or more since little or no load is being placed on the battery by the starter. A too-tight engine, or a shorted starting motor will place a HEAVY load on the battery which will drop the terminal voltage down to 9 volts or less. Armed with that information, the rest of your diagnostic procedures will take a drastically different turn. A "new" starter doesn't necessarily mean it's "good", but guessing and swapping parts without a detailed diagnosis rarely if ever works out well.
Edit: I just reviewed the photos again, and Joe is right on target. Dump the Mickey Mouse battery disconnect, and either fabricate a heat shield between the starter and the header, or go to one of the gear reduction "high torque" starters available on Ebay to get more torque on a hot start. It's a definite possibility that the starter armature is getting heat-soaked by the exhaust and is getting enough drag on the pole shoes to try to lock itself up after a fairly short drive. I've got a crippled leg, but I'd probably be able to outrun anyone who tried to GIVE me a set of headers if I had to run them on a street engine.
