I asked a few Toyota guru's I know about this.
their take is no the two are not remotely the same.
You do know their are a few different vetsions of the A340?
Not all A340's have removable bellhousings, some are molded as part of the overall case.
If theres any chance at all of having this case TIG welded you might go that route, many have done this repair already, make sure you strengthen the case on the outside where extra material wont create a clearance problem.
As far as finding a replacement, ever heard of "Hens Teeth"? Yea youll find your replacement sitting on a shelf next to them.
Most experts report a trans failure is the leading reason for engine/trans swaps. Chevy 4.3 with a 700r4 is the most common replacement.
At the best of times even on new equipment toyota trans replacements and parts are hard to find, they dont fail alot so aftermarket parts dont generate a large market, why replace whats not broken especially if your beating it and its still not failing.
After 30 years of beating Toyota 4x4 trucks I can count the transmission failures on one hand.