3 more 12 volt rewire questions

1. This should work fine. The wire from P1 that you would normally connect to the lamp (or diode or resistor) would be directly connected to the ACC contact. When you turn the switch on, the ACC is connected to the battery. When you turn the switch off, the ACC is isolated from both the battery and the IGN contact. The switch is performing the function that the diode would normally do.
2. The alternator will start charging without the lamp because it's getting its excitation from the ACC contact on the switch. You won't need anything else in the circuit between the P1 and the ACC contact. P2 on the alternator should still be connected to the battery -- either right at the alternator or with a wire run directly to the positive post of the battery (this is why many positive battery cables have a smaller diameter wire connected to the clamp).
3. The operation of the start button on the transmission can remain as it was.

Note that #1 and #2 above mean that you won't have an idiot light to indicate whether the alternator is charging or not. Since you've probably got an ammeter on the tractor, this isn't a big deal.

Use your 6V starter and selenoid. Don't bypass your trans start button (safety, starts in neutral only) Get a 3 wire alt (cheap about $20+$15 core) plus the two wire pigtail for the alt. Take your generator mount and install backwards and a strip of metal about 2-3" long to bolt to the end of the of the slotted adjuster and the engine to extend it. I use the red dash lite instead of a marker lite or diode. These are to keep juice from feeding back to your ignition causing the tractor to continue to run when you try to shut it off. Get a 70s VW(any model car with 12V resistor coil)coil and remove all resistors from lines from terminal block to coil. Hook the coil up with neg- towards the distributer. Wire according to this diagram and install a 12V battery with neg- ground. A smaller pulley would make it charge from start up, with the larger pulley you have to goose your engine to get the lite to go out(charging) but I've notice that once goosed it charges at idle and subsequent start ups in the same operating time.