First: The stock, ribcage four speed in a Sprite is a nice little trans. If you need good cruising for a street car, the final drive from a newer car can give you 3.9 or even 3.7 (as opposed to 4.22). For a street car, that would be a simple and effective path to follow.
But yes, the
~Frontline~ kit that JP refers is available for "A" series and 1500 Spridgets. The Ford Type 9 is an OK trans...not super great. They come in the US import "Merkur".
Honestly, I think there's an opportunity for someone here:
There are tons of Miata transmissions available and they are skinny enough to fit in a Spridget trans tunnel. They are a better trans that the Ford 9 or the Datsun and can be found for $200 easily.
The Miata trans does not have a removable bellhousing and the flywheel is small diameter. This swap would probably require a Miata flywheel modded to fit the Spridget crank plus a redrilled end plate on the Spridget engine (to accept the Miata pattern). Figuring out the starter might be a tricky job.
Still, I think it's an opportunity....
<span style='font-size: 8pt'>Then again, if you're putting a Miata trans in your car anyway, why not include that lovely little twin-cam engine that it's *supposed* to fit....<runs and ducks> /bcforum/images/%%GRAEMLIN_URL%%/jester.gif </span>