My seats are killing my back too in SoCal traffic. I tilt my seat back to not hit the headliner.
Were your 4runner seats manual or power to begin with? (My guess is manual since SR5)
I just bought the same seat this morning as a test too. My 4R seat is manual. I saw someone on youtube wire similar seats to manual seat car so I was game to try it.
Are your seats higher or lower than 4R seats?
I'm looking at lowering overall seat for more headroom since my head hits the headliner. I might need a welder to make a custom bracket for me.
Are make any progress on your seats?
Sorry its been a while since I came on. I bought a 5th gen last summer prior to moving. My 3rd gen is at my parents house in NJ.
The bmw 3series seats had their own wiring harness. I hooked them up directly to the fuse box and grounded inside the car. I tested with a portable battery jumper when I picked up the seats. They are full power, heated and have a lumbar controller. Heated was an ordeal to get it to work. I used bmw heat switches and had to test different combinations and look through schematics to get it to work properly.
They are higher than stock. I cut the mounting feet off the old rails and bolted then to 1/4” cold rolled steel bars to make my own adapters to fit the bmw sliders. It worked and is solid but it raised the seat. I’m 5’ 8” so it wasnt terrible. My brother is 6’ 1” and he has a hard time in there. Bmw seats are also firmer so you dont sink in. Id say there is at least a 2” sitting difference. I probably should have just found another 3rd gen and bought its passenger seat to take the bottom foam and done wet okole covers and called it a day. Leatherique doesn’t hold up well. Looked and felt great after proper application but my experience is not a good one.