Alternator wiring harness has a large lead running to the starter, connects to the battery post on back of solenoid.
What is the purpose of this lead? Is this where the generated dc feeds back to the battery?
Can I move this lead to a terminal that leads more directly back to battery?

Yes, the purpose of the heavy wire is for powering the system and charging the battery. You could move it towards the battery but no need to since with it's connection to the starter, the cable makes a concise connection to the battery.

Why do you want to connect it directly to the battery?

My battery is in front trunk. Runs through a cutoff switch in dash, come back to a terminal near the relay board. From there, another lead runs to starter. My thought is that lead from alternator could connect at that terminal, bypassing the few feet of lead running to the starter. Makes for a cleaner install of the aftermarket hi torque starter.

My gut would tell me it is connected to the + terminal on the starter is due to the shorter distance as opposed to a longer distance to the battery.

Given your battery is in the front would make a stronger case to keep it connected to the starter. The power makes it back to the battery either way

The alternator output wire needs to connect to the battery side of the cutoff switch. If you connect it to the other side, your cutoff switch won't kill the engine if it is turned. The alternator output will keep it running.

Clay, sounds like it's more an anti-theft thing than a safety cut-off thing. If it's a safety cut-off I'd wire things differently.

Apologies, I'd not noticed before that Randy posted here. I replied the following on Facebook, with minor format edits:

The only really big wire you need is from the battery to the starter; that's the highest draw your battery will ever see.

The next largest wire you need is from the alternator to the battery, with that wire sized to cover the alternator's max output. This wire has two functions: recharge the battery and supply power to the car's distribution system when it's running (with the assumption that a large chunk of the alternator's initial output goes directly to the battery, to recover battery discharging from starting).

Once the battery is recharged, the battery becomes nothing more than a power/voltage dampening component (and a source of power if the alternator fails); you could use a capacitor for that running function.

So here's the rub, though a minor one. If you move the alternator charge wire directly to the battery, without intersecting it to the starter lug in between, then you're making the alternator output go all the way to the battery and then all the way back to car's various discharges (such as that OE distribution block).

This is why you see a direct large wire from the battery to the starter (highest load) and then generally the recharging alternator wire is commonly connected to the starter terminal; the battery wire from there is large enough to handle the alternator's left over output back to the battery. The car's distribution block will then connect somewhere in the system to get access to both battery and alternator, location depending on car layout. This way the alternator can simultaneously recharge the battery and cover the amperage loads directly to the car.

Now, given the amount of amperage we're talking about on a 914, it's not massively important. But doing it like described above does create extra amperage loads in the battery circuit (and additional fatter wires) that would not normally be needed. Not a terrible thing but also not necessary.