In doing research for a possible engine and transmission swap, I have been looking at different adapters to adapt different transmissions to the stock Toyota transfer case in my '81 FJ60. Everything I've found says the split case in the FJ6 all use a 19 spline input, but there were some slight gearing, oiling, and idler shaft changes throughout the years (not to mention the vacuum shifter on the FJ62). I called Advance Adapters to ask some questions about their adapters, and the guy there told me all the Land Cruiser adapters were actually manufactured by Mark's in Australia. I had already found a 6L80 to 19 spline Land Cruiser adapter on Advance Adapters' website, but Mark's website only lists that adapter (I'm assuming it's the same based on what the guy at Advance told me) as working with a 5 speed transfer case. I emailed Mark's about using the adapter with my early 4 speed transfer case, and the guy there told me the input size and spline count on my early case was different. Can anyone verify or explain to me why it won't work and what I would need to do to adapt my early split case to the 6 speed auto? Do I need to just buy a new transfer case? It looks like they are still available new from Toyota. Is that my best option?