Most Bosch alternators are very similar internally, Take some measurements and see how you go. You will have to use the same rotor and stator/rectifier out of the bigger unit.
I converted mine with what I believe is camry internals just from bits off the shelf at work and it peaks at 100A fully loaded..
Do you know if it is an externally regulated alternator? I've seen diodes let go in the alternator and they backfeed and hold the reg on causing the drain..
If something is draining the battery you should really find what it is and fix the problem. If you don't isolate the second battery when the car is sitting the same thing is going to happen to it too.
Unless the alarm came with 2 separate wires to go to indicator left/right they are usually set up to only flash the park lights on and off when you arm/disarm.
you can get tricky and use some diodes to make it work on both indicators but it all depends if the unit is capable of that much current draw through all the globes (It can burn out the transistors inside the alarm)..
Intensity of the spark is due to the field collapsing faster, That's why transistorized ignition systems are better for this sort of thing. Do yourself a favor an invest in an electronic dizzy..
Slant front has park light and indicator, Flat front only has park light.. So that is the difference, Cross those two and you will have indicators going on park lights and park lights going on indicators..
Should be able to buy them new and yes you can get them recoed depending on whats wrong with them..
Check you have wired it right, Ignition, Lamp and sense..
Put a meter on it and see if it is charging..
Fuel level senders work on a resistance reading, Basically you take the fuel level sender wire to frame and the gauge should get full deflection (empty to full) and stay at full till you take the wire away from frame. Thats the easiest way to diagnose if your fuel sender is at fault or the gauge..