After a late night (I tend to tear the truck apart even when I have to drive it to work the next morning) and a weekend, the BMW seats are in, functional, and quite comfortable. Here are some build pics.
Here is the floorpan with the carpet pulled away. You can see the big hump that runs across the floor. You could mount the new seats on top of it, but my head would hit the ceiling. So it had to go.
I cut away the spot welds with a cutoff wheel on the angle grinder, being very careful not to cut all the way through the floorpan. There was no turning back after this point. But hey, it's paid for!
No more hump.
Hit the bare metal with some primer, plugged any open bolt holes with silicone, taped the wires into their new positions.
Pulled the wires through to power the seat adjustsments and for the driver's seatbelt sensor. On the bottom of the BMW seats, there are a pair of heavy wires, brown is GROUND and red is +12v.
Okay, I forgot to take some pics of the adapter fabrication, but basically each seat has two straight pieces of 1" x .125-wall square tube, running left to right. The front one is tapered where it meets the transmission tunnel. The adapters allow the outboard seat slider to be positioned about 1" over the door sill trim.
The rear adapter. On the inboard side, there are spacers between the adapter and the floorpan. I just used some big 2" square washers. On the outboard side, I bolted the adapter to the existing tapped hole in the floorpan, using the original bolt. For the 3 other bolts that hold the adapters to the floorpan, I drilled through the sheetmetal and backed it with fender washers.
The outboard side of the drivers seat. All the electric adjustments work, but I haven't been able to get the memory function to work. Either I just don't know how to set the memory, or it needs to be connected to the BMW computer to store the settings. I push "M" then the "1" to store the position but it just goes back to the old "1" position.
And the finished product:
I am working on some flaws with this transplant, I'm happy to hear suggestions:
1: no longer have a passenger seat that flips forward for extracab access.
2: If seat is too far forward, the control panel hits the door pocket preventing it from shutting. I may have to trim the door pocket. Fortunately it's only an issue when my wife drives.
Benefits:
1: Excellent seats!
2: Gained a huge chunk of real estate between the seats where the useless bench was. Plan to add a large center console with internal 12v and 120v AC inverter outlets, storage for go-to items like camera, ipod, radios, snacks etc.