Re: 35 spline?
Not so sure about 35 spline. I don't know if 31 spline axles are large enough diameter for a 35 spline cut. I know 31 spline axles and gears are very common though. For your Toyota, 31 spline is plenty. Even with the big tires your vehicle is light enough to not have any problems, as long as you have the 4 spider gears in lieu of the 2 gear setup.
I currently have 28 spline in my 71 Bronco and have put 350 hp to 35" tires without any problems. I have trashed the teeth on my side gears because of the 2 spider gear setup. This was from putting my foot into it, and spun the tires going around a corner (the tires were obviously spinning at different speeds). This has happened several times, but never broken an axle. In my opinion, 35 spline axles are just a good way to add weight to your vehicle.
Also, I think the 31 spline axles require a larger bearing that may not fit in your axle housing without a conversion from someone like Curry. You may want to look into it.
Hope this helps
P.S. I may go to 31 spline (just have to see how much money I can round up). Please let me know what you decide.