2002: 120 Series Prado/Landcruiser and Gen4 4R appear on the brand new 120 platform.
2005: The Tacoma is replced with a new vehicle based on the 120 Platform. Obviously the rear frame section is adapted as a pick-up configuration.
2006: The FJ Cruiser is introduced, based on a 120 Series chassis.
2009/2010: The 120 Series (Land Cruiser) Prado and Gen4 4R are replaced with versions based on the brand new 150 series platform.
I can tell you that the GX470 does not share a wheelbase with the 4runner or FJ Cruiser. I built mine and all the measurements are just a bit different.
The sliders were not matched. The rear suspension had to be removed (airbags) to add spring perches and coils. The front was s traight up FJ/4Runner/tacoma so the total chaos uppers and iron man went right in. I found out the CVs are interchangeable, but the tie rods are not (broke both offroading).
I do agree with what people are saying. The sheetmetal, sound proofing, and tight build of the GX nets 10 cubic feet more space than the 4runner. I have third row seats but they are for kids only (too small for adults). It has V8 power, but I think the IFS is a bit under the task of holding up to it in serious offroad situations. I found the limits last weekend (CV, tie rod) but I drive hard.
Nothing the SAS I am going to do won't fix.
Oh, and there are not many options for bumpers, sliders, snorkels, etc. You need to be smart. I sourced a Prado Iron Man bumper, snorkel, and suspension from Australia. There was a lot of cutting involved to make the bumper work. Don't think it is a bolt up part (yet). I am working on this to see if there can be a GX bolt up aftermarket kit.
I am about to SAS the front with a custom axle since I wheel too hard for the stock IFS setup. Also building a custom rear with tire carrier and jerry can holder.
Should be an adventure! Oh, and anything I get done will be able to be ordered for your GX soon. Working on that part