Overview
The G97 series transaxles are from the late 997-series 911s. As such, they are among the latest, and strongest transaxles from Posrche. They are characterized by larger crownwheels, stronger gears, and stronger synchros than their predecessors, the G50 series.
These are typically great choices for an SL-C, and can handle large amounts of torque, especially if the torque is smooth, and the vehicle is not subjected to drag racing.
This series is normally available from wrecking yards or rebuilders, as new units are very expensive.
The factory 01 car with power from 550 to 700 HP ran the G97/50 during it's racing period, with good results.
Sources
Like the venerable G50-series, these transaxles are widely available from local boneyards, specialty Porsche-specific wrecking yards, several different re-builder shops including Gbox, California Motorsports, and others.
Technical
The G97/50 is from the turbo variant, and represents the strongest choice from the normal 911s.
GT2 and GT3 variants are much rarer, much stronger, and much more expensive. Look for these if you are building a mega power SL-C, or just want a much more race-oriented box for your car. These tend to be hard to find, however, so take your time looking for them.
Starters, clutches and flywheels are available to make these units work with the popular LS V8, but other engines will need custom adapters, and possibly flywheels, etc.
Superlite has adapters for this series of transaxle.
Issues
There are few issues with this transaxle for most LS engines, and there are many cars with decent power running these with no problems. Problems are that parts, especially for the GT2 and GT3 variants are rare, and expensive, and there are relatively few people really qualified to work on them. But they really done need much work beyond the normal flipping kit.
Ancillaries
Many different starters are available, both Porsche and aftermarket. Clutches, and flywheels are also easy to source, and can be targeted to many different levels of power.