Simply put, 0.5:1 is a really excellent overdrive ratio if you have something close to 400 hp and a 3.73 rear end. My GTO with T56 will climb every hill I've ever encountered in 6th gear, which is 0.5:1, without downshifting.

In my opinion, an overdrive of 0.74:1 or close to that just isn't enough help to reduce engine rpms at highway cruising speed with a 3.73 rear end.

Here's the engine rpms from my car with T56 trans and 3.73 rear end at 70 mph:

4th gear, 1:1, 3250 rpm.
5th gear, 0.74:1, 2700 rpm.
6th gear, 0.50:1, 1800 rpm.

These are actual speedo and tach readings that are slightly different from theoretical (for example, 1800 is 0.55 x 3250).

Bottom line: a Passon 5 speed will only give you about 0.70:1. But it's a direct bolt in with no modifications. A T56 6-speed will give you 0.50:1 but modifications are needed.

The T56 does have two places to put the shift lever. It has a hydraulic slave/throw out bearing. Highly recommended: ventilate the bell housing with openings for air in and air out to blow the clutch dust out. Otherwise the slave may fail from the abrasive clutch dust. My closed tight system failed at 20,000 miles, and I added the ventilation with a new slave. Also recommended for T56 is the tickperformance.com clutch master cylinder kit and one person clutch bleeder line.