The T56 Magnum is a popular conversion with 03/04 Cobra owners due to the increase power handling. While it’s a mostly bolt in swap it’s not 100% bolt in. A few items need to be addressed.
It should be noted the housing of the T56 Magnum is 1 5/8” longer than the stock T56. This will require shorting of the driveshaft.
The stock output shaft is 27 spline. The Magnum is 31 spline so you’ll need a new yolk for the end of your driveshaft too. You’ll need a D93 yolk for a 1350 joint. The part I used was: Sonnax p/n: T3-3-2491HP. It’s a nice billet piece and not a cast yolk.
The ribbed splines on the front of the case are thicker on the Magnum giving less clearance. I found when installing thicker clutches like the twin disk RXT you don’t have enough clearance for the clutch fork. A little bit of clearancing on the clutch fork with an angle grinder fixes it right up.
You’ll also find the rear transmission crossmember bolt holes don’t line up 100%. This requires some light slotting of the holes on the transmission crossmember.
Also note the Magnum will ship with provisions for a mechanical speedo cable but does not come with a block off plate. Just a rubber plug as shown here. You can find some nice billet block off plates on Ebay for very cheap and close it off.
The clutch for dust cover has no hole provision on the Magnum casing. You can easily just drill and tap one.
The stock bell housing will work just fine.
The transmission tunnel may require a little clearancing right by the shifter bolts. For many, myself included, it had a very slight rub. Just barley enough to have an irritating vibration noise.