Starter stays engaged ONLY in park???

Righty Tighty said
the seatbelt interlock has all been removed.

OK. I was actually a little uncertain about this since early in the thread you wrote that you disconected the interlock.
Orignally there was an interlock switch in the engine bay. This I think has the emergency bypass switch in it and is the one you disconnected?
I didn't show it in the schematic.
There also was another interlock box in the cabin. It may have had some other funtions too. I showed that with dashed lines. Is that still connected or is it gone?
Is the connector still there?

Righty Tighty said
The new harness coming this week will have all the factory interlock wiring, so if I need to I can do a "proper" bypass.

Again a little confusing to me. In a post Dec 17 you wrote that a new engine harness was en route. A couple days later in the post showing the ring gear teeth, it seemed that you had installed a new harness. Are you now getting an instrument panel harness?

Righty Tighty said
With the higher than normal resistance between the power in red and yellow starter wire, how do I find the cause?

If you have a good connection from the battery, you can test as outlined above in post #82.

Without a good connection to the battery, then check resistance in each key position. Do that with probes in the steering column connector.
Like Tooljunkie, I'd not be doing hot tests until I was a little more certain about where the hot wires are connected and that no loose conductors can contact ground.

Mattax said
One probe on the power in red (12 ga) use the other probe to check the Ignition start, Ignition run, Accessory, Starter relay.
Key off, they should all be open circuits.
Key in Start, there should be little to zero resistance to Ignition start and Starter relay.
Key in Run, there should be no resistance to Ignition run or Accessory.