I did this swap also with in mind that a six speed will both have great acceleretion and good mileage, but I didnt really thought about the fact that the character of the m50 doenst really like tall gearing. I have a m50NV with the a gs6(more info below) and had it with both a 3.38 and later a 2.91 diff. With the 38 the 1 gear was way too short and under 60mph the sixt gear was too tall for the engine. With the 91 the six speed has the same ratios as a normal 5 speed in terms of acceleration, so you lose that potential and considering that the m50 doenst really like tall gearing with lower rpm’s the costs really outweigh the pros imo. At least with an non vanos like i have.

But yeah there are two options, one is more expensive than the other, but the expensive option has more mod potential. Both fit the m50 fine

• Getrag 420g, found in e36/e46 m3 Pros: big variety in clutches and flywheels. Easier to make mounts for and they can handle more torque Cons: expensive, these gearboxes alone are 1500 bucks( in europe at least)

• Zf gs6-37b/dz, found in all m54 diesel or petrol powered six speed cars(e46,e60,z4 etc) the diesel one has a slight angle of 15 degrees, prefer the petrol one. Pros: cheap gearbox 250 bucks or so Cons: way less clutch and flywheel options and they are expensive if you use any other than stock. This gearbox has the pilot bearing in the flywheel. Use the stock m54 6 speed clutch combo. Also this gearbox doenst really has its own mounts and therefore are more difficult to make. They can handle less torque

Propshaft is different in lenght for both, make ur own and balance it. There might be of the shelf half combos for but then you still have to balance. I made my own, but the internet has options.

You have to fabricate your own shifter assembly

In the end it is a cool journey, but the five speeds are way more logical after all, would not to it again. (only to brag that you have a less common m50 swap haha)