I know there is a few people that have swapped out the front subframe for the fc one. Assuming the factory 1st gen axle is used what are the driveshaft onptions?
12a driveshaft? SE? 2nd gen?
Or is a custom length needed?

Depends on what transmission you're gonig to run. If you're keeping a NA trans (FB or FC, either way) then a stock driveshaft matched to your rear end will work.

If you're going with a T2 trans then you'll need a custom driveshaft, but that would be needed with or without the FC subframe.

FC driveshafts are way too short and won't work.

Short answer: the FC subframe doesn't change anything as far as the driveshaft is concerned unless you put the subframe in a different position (to alter wheelbase or something like that) and even in that case I'm not sure it would be enough to alter the driveshaft length...

If you mount the axle centerline to be the same as FB, and use an FC engine, the engine will be in the exact same place as the FB engine, so the transmission does not move and the driveshaft is the same length.

If you shift the subframe forward like I did, you make new motor mounts to keep the engine in the same spot.

As it was mentioned, it all depends on where the engine will end up (where you want it) and the transmission choice you are going with. However remember that getting a new driveshaft made or shortening one is pretty easy and inexpensive (couple to a few hundred). So don't let that be the limiting factor of moving the engine back!

Here's the neat thing.

It looks like the FC driveshaft is the same distance shorter as the SA shifter is further forward than the FB shifter, and that the FB motor mount position is further forward than the FC motor mount position.

Yep, I think I can get 6" of engine setback with all factory parts. The tricky thing will be hacking the firewall so that the carb clears, while still keeping the heater core. The oil filter will have to be remote-mounted and access to the slave cylinder will go from "mildly annoying" to "wow this sucks".

Alternatively, I think I can use this to put a T2 transmission in with an OEM driveshaft (instead of a $$$ custom one) and just have to use a cantilevered shifter like a Cobra. The center console and stock shifter console would have to go, but, well, I've been wanting to put that SA dash in the car anyway. (Yes, all this is preferable to a $500 driveshaft)

I've got a t2 motor and trans in it already. With a custom driveshaft made up. My steering box is shot. Finding a used one still good is slim and I can swap the subframe for cheaper than a new/reman box. And i like the fc setup better.

Sounds like exactly my rationale for doing the swap. It was cheaper than fixing the worn-out parts in my FB suspension, and I could get better struts.

How much wider is the track? Do the wheels still fit under the fenders?

Had my driveshaft made for about $350. Btw

Track width is the same. Using ZX2 strut tops, I had positive camber just like stock FB.

I have four Progress camber bolts, and much-modified FC strut tops that change that. FC tops have a 4mm larger bolt pattern than FB, so when I altered them to fit, I did it in such a way to increase negative camber.

It's amazing how the more you look at them, the more it's obvious that the FC isn't all that much different from the FB. Most of the hardpoints are the same or only moved very slightly, the major changes are either superficial or rear suspension related.

Then you figure that the FB/SA were largely cribbed from the RX-3...