Thank you for the detailed response. It reinforces what I imagined. My brother had an 85 4Runner that he built for rock crawling and he had dual marlin crawler transfer cases (4.7:1 doubler and 2.28:1 stock). It was really slow in double low range and 1st gear, but seemed overkill. He was able to idle through just about anything he pointed the 4Runner at though.
Did the doubler increase drivetrain noise while on road driving/highway? What was your total cost if you don't mind me asking? This does seem to be a more reasonable/economical way to get a doubler.
Not really any added noise while driving in hi/hi. Sometimes and certain RPM's, on of the triple sticks would occasionally make a tiny rattle, but I'd just nudge it and it would shut up for a while. It makes lo range noises in lo range, and double the lo range noises in double low range.
I had to look it up, it's been a while (first paid last November), but I got some sort of pre-order discount for ordering before they were ready, thus the long wait. $1399 for the doubler setup and the very nicely made triple stick setup.
Then a couple of ordinary plain old PnP donor transfer cases. I got two because I wanted to have it all set up on the bench and ready to go on, vs. taking mine off and having the truck not running until it was completed. I think I paid maybe $50 a piece for the two transfer cases? The planetary (middle) donor could be from a wide range of mid 90's - mid 00's Toyotas (Tacos, 4Runners, Sequias, Tundras), but I had to find the right rear case donor, the same h-pattern case as I already had.
Then some custom length driveshafts, about 6 inches difference front and rear (I think my wife's MC setup was something like 8.5 inches). IIRC those were around 800-ish.
And that's really it. I bench assembled the NWF kit with the two donor boxes. Initially I was under the impression that the rear box sort of bolted right on, very few changes, but really, it had to come apart slightly more than the middle donor case did - since you need to replace the planetary gearset input shaft in that box. For the middle donor, you just strip it down to the stock planetary gearset and put that in the new case as is. So you are really stripping both cases *WAY* down. Not too difficult though. I had to do it twice because I *ahem* forgot a little ball bearing that goes on the input shaft in the rear box that locates something circlipped onto it. I discovered this after it was almost all the way together, and had to tear it 99% of the way back down, lol.
Then once the driveshafts arrived, it was a really quick process to pull my t-case, leaving the trans untouched and in place, and then slide the new setup in place. I extended some wires for the sensor on the rear case (the car doesn't know about the middle case), bolted up the driveshafts, and then sewed up a new shifter boot for the triple sticks and installed it.