This post will show you what you need to do to actually get the transmission in. There is a good amount of modifications required, I was going in blindly thus couldn't do and document changes until I saw the need for them. You should make these changes before the transmission is in, all the pictures are in chronological order. Please keep in mind picture per post count requires me to split the install pictures into multiple sections.
Required bolts for Transmission mounting
Stock Transmission Mount Removal
Spot weld remover will make your life easier here, I don't have one and figured grinding the mount off would help the frame keep it's rigidity.
Rest of the transmission mount modifications will be posted in a separate post, reason I'm posting them here is because it will make your life a lot easier removing the stock mount with no transmission in place.
Another thing you want to do before the transmission is in place. You can see how much more difficult it was to do this once the trans is in place.
Driverside Rear Subframe
There is also a bolt that will sit right above the subframe. You need to notch the subframe or replace this bolt with a low profile bolt. Since I can't get to this one with trans in, when the engine moves back under full throttle this bolt hits the subframe. You can hear and feel when that happens, this also overtime will destroy the bolt.
Driverside Front Subframe
There is a lip on the front of the subframe. This will prevent you from inserting the axle into the transmission. If you do some how manage to insert the axle, it will be destroyed as soon as the axle spins.
Shave, test fit, shave test fit. NOTE: To test fit the axle and to make sure it goes all the way in, remove the axle's C clip. Once your sure of you are done, reinstall the axle's C clip.
To reinforce it and prevent water from getting in, you should weld it.
Except that will hit the axle again, thus get the grinder out again and grind it down, try not to grind too much, otherwise you will have to reweld any holes.
Another thing I did is flatten the axle zip tie head
Fairly close to the subframe, so far (over 500miles) it doesn't seem like there is any contact
Now we can actually try to get the transmission in. Since the transmission is much bigger, clearance is a big issue. At one point after about 2 hours of trying to get it aligned right I was kicking the transmission which magically got it in!
I could lift the old transmissions by bolting the chain to the motor mount points, this wont fly with the bigger 6 speed trans. I had to find new lifting points
You will probably have to unbolt the lower control arm subframe mounting bolts to get it out of the way.
Slow and tedious process, and least you have a window to see how far the input shaft is from the clutch disc.
Since I didn't shave rear of the subframe ahead of time, this was a very painful process. I should have dropped the transmission and grinded this off, but somehow I force it in.
Now the input shaft finally was able to align with the disk
With some kicking I was able to force it in
Once it's bolted up you can remove the hoist and get to working (I'll post bolt sizes later)
Bolt up the starter too. I was able to get away with using one OEM starter bolt.
Steering rack clearance is tight too.
Now that you have the transmission in place, you can work on installing the motor mounts and axles. Rest of these steps assume you have the motor/trans mounts and axles installed already.
Hook up the speed sensor
Here is the harness for the reverse and neutral switches
Shorter one goes to the reverse switch (blue sensor)
Longer line goes to the neutral switch (black sensor)
Find a good spot for the frame ground, can be seen to the right of the wire harness
Battery tray will need to be cut a little
The Axle dust cover will rub and needs to be cut down
You can see where it rubbed for me, cut that whole section off.
Should be good after that
Filling transmission with oil
Loosen the fill plug with 10mm hex Allen socket
I used GM Syncromesh, you need about 2.4qts, used a pump to get it in, hard to get to that fill plug otherwise.
Keep filling until some comes back out, then stick your finger in the fill plug and feel for the oil, if you don't have any on the tip of your finger fill more.
Install the boot for the TOB fork
Install the P12 or Maxima (needs to be modified) slave cylinder
That's it for transmission modding/installing. Put everything together and go for a test ride!