October 2013:  One of the benefits of turning the engine longitudinal is that a strong transmission can be mounted to the SBC.  In transverse, the older Getrag was required (see here).  After upgrading to 425hp, the Getrag would defiantly be a weak point.  I did quite a bit of research on what transmission is commonly used in this situation.  The 2WD Audi is common choice by many, but they are becoming harder to find.  I also had concerns about their ability to handle 400+lbs of torque. 

The Porsche 915 is the entry level option, with the 930 being a much stronger upgrade.  The best option is the G50, but that is also the most expensive option.  To make a Porsche transmission work in a mid-engine configuration, the ring-n-pinion gear needs to be inverted so there are not 5 speeds of reverse.  I found this 915 on eBay pretty much ready to go.  It had upgraded 930 spindles, a flipped RnP gear and a limited slip differential.

In order to mate a SBC with a Porsche transmission some conversion kit it needed.  The most popular is the kit from Kennedy Engineering.  My transmission came with the kit, but i needed a new pressure plate.  The folks at Kennedy were great and got me all setup.  I also chose their high-torque starter. 

In order to transfer power from the transmission to the rear wheels, I had drive shafts fabricated.  This is often another weak point with high torque engines.  The axles are shortened versions of what would be on a 1-ton truck.  They are bigger than what I wanted, but still work.  The folks at asdfsfsf cut and balanced them.  I simply welded the ends of the u-joints to a mounting plate for the transmission and half of the CV joint for the rear axel.

The last part of the conversion requires a new shift kit.  There are a handful of available options.  One draw back of the Porsche is that the shifting mechanism is now in the back of the car.  There is also limited clearance under the rear bumper to mount the shift brackets.  I decided to go with the shifting kit from ShiftCable.  They helped me fabricate a mounting bracket that cleared the rear bumper.  Aesthetically, it is not great, but will have to do.