I have a TKO in my hatch and a T56 magnum box in the SLR. Neither floor has been cut, and both cars have the original consoles fitted. The T56 defently fits the tunnel better than the TKO. Both boxes shifters line up with the original shifter hole in the floor. The T56 magnum box need no mods to go straight in unlike a commodore version which will need the extension housing changed to suit.
Both gearboxes have electronic and cable speedo drives and I use both on the two cars.(electronic engines and original mechanical speedo) The tail shaft angle is better with the T56 but not perfect. I don't have any noticeable vibrations with the T56, and the only noticeable aspect that the angle isn't perfect is a very slight rumble when I back off on over run. I have taken it up to 160km and have a 3.9-1 rear axle ratio, 17" wheels. No one ever notices it but me, I know its there. I still have the original upper and lower rear control arms so the diff angle has not been adjusted. If I forked out for a set of adjustable top control arms I could possibly make it better. But it just not enough to get worried about. If I had the car lowered more at the rear I would defently need to improve the drive shaft angle.
The TKO angle is less than desirable. The hatch is lowered considerably more than the SLR and is still running 14" wheels. I fitted rear upper control arms to improve the angle and although I found a sweet spot on drive I had vibrations and a rumble on over run. I ended up putting in a two piece tail shaft which has eliminated the vibrations and the over run rumble, however the engine has truck loads of torque and around 500hp. With 265x14 rear tyres there is reasonably good grip and in first gear if I bury the throttle hard the centre bearing loads up and I can hear a slight rattle as the rubber bottoms out, this is due to the working angles at the CV joint. Again is not bad enough to get to excited about but its there. The Hatch excites the rear tyres very easily when provoked but I rarely punish it much these days.
I have had a few oil leaks with the TKO from new. The top lid needed to be resealed. The front cluster cap leaked, and I have replaced the output seal a couple of times. The rear extension housing bush is perfect so I don't know why they have been a problem.
Driving wise the T56 magnum box if far superior. I used to think the TKO shifted reasonably well till I put the T56 in the SLR. The TKO feels like a truck gearbox when compared to the T56. The T56 is also rated at 700hp which is a fair amount more than my TK0500. Both gearboxes were purchased brand new. I purchased the T56 from Summit racing in the states and cost me around $4,500.00 from memory landed to my front door. I think DHL charged me some sort of government tax around $300.
In summery the ratios are much better in the T56, the shift is an absolute dream to change gears, its a better fit in the tunnel and a stronger box. The only down side I can see is the T56 costs a bit more and a few more kg heavier. I haven't had an other problems with the TKO other than the few oil leaks but if it ever shit it self I wouldn't rebuild it and would be happy to put the T56 magnum box it too.