Personally, I wouldn't spend the money on either, unless you are really bent on keeping the stock transmission. As Kwai pointed out the options for better transmissions are there, and you could go with an overdrive at the same time for better road manners. Plus 2WD transmissions are a bit more plentiful too.
That is the only reason that you'd need an adaptor kit. Like Jon said, just make the mount plates and you can pretty much bolt in anything to the stock frame horns then.
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