Swapping a transmission/motor: Input shaft resolution??

So I am pondering an engine swap. But staying short of the details of the swap I am curious how the input shaft on the tranny is spun if the new motor uses a different spline size/count or is a different length from the tranny than the old one was.

Example (because it's popular):

Say I am swapping in a Chevy 350 and using my current tranny.

I know there is a magical adapter plate that allows the tranny/motor to bolt up.

But, how is the tranny coupled to the new motor? Is the flywheel/torque converter modified? Is there some sort of magical coupler that is custom made to adapt to each side of the setup? Is there a custom input shaft? DOES IT WORK BY MAGIC?!

Thanks!
Morgan

:lecture: Automatic transmissions have a splined shaft that plugs into the torque convertor which in turn is bolted to the flexplate. Of course the flexplate is bolted to the crankshaft.

Manual transmissions have their power transferred from engine to tranny through the clutch pack. Again, the transmission input shaft is splined and plugs into the clutch disc which is pressed to the flywheel (which is bolted to the crankshaft) by the pressure plate which is bolted to the fly wheel. The clutch disc is sandwiched between the flywheel & pressure plate.

To make the engine bolt up to the tranny, you'll need a bell housing or an adapter that matches the bolt patterns of both, or find an adapter plate. If the shaft has different splines, you'll need to either replace the input shaft of the trrnasmission or use a spudshaft

For much greater detail, try http://www.advanceadapters.com

Thanks. I did know how the basics work, I was more concerned with the actual power transfer between dissimilar input/output units.

I did check in on the AA site, but didn't see anything about the actual power adapters, but frankly I didn't look seriously hard as I figrued they wouldn't have much of an explination.

What, pray tell, is a "spudshaft"?

Thanks!
Morgan