Yeah, that was me attempting the 4G63 into my GT. I ran into some serious issues with the project and the idea was scrapped. The main problem was finding a RWD transmission that would work. The only RWD tranny that will bolt straight on to the 4G63 is the 5-speed found in a few rare 2-litre Dodge D50 pickup trucks. And not only that, but they only fit wide-block 4G63's, most that you find in DSM's will be narrow-block. Then not to mention, you have to go and find all these parts in a junkyard yourself, which is impossible when you're like me and live in Canada and all the wrecked cars are in the States. What are you going to do, ask people to go to junkyards for you, remove a transmission and ship it to you? I don't know anyone that would know the first thing about Dodge D50 transmissions or even what a D50 looks like. So then there's the option that Eric Plebani patented, and that's taking this one tranny (I forget the name of it now) and dumping all the internals and then swapping the Conquest / Starion transmission internals into the housing. But guess who's the only one that knows how to do it? Eric Plebani himself. And good luck getting a hold of the guy. So then there's option 3, which is use the W58 5-speed from the Supra - a favorite among old European car restorers. Some guy in Orlando came up with a custom bellhousing to mount a W58 to the 4G63, but guess what! No one can get a hold of him anymore. So in the end you're left with option 4, which is to go to Dave Buschur and buy his Powerglide kit for around the area of $4,000 usd. And then you're left with a 200 pound transmission with only two speeds, the only thing it's good for would be drag racing.
Oh, and that's just the transmission problem. You run into a new problem if you try putting the 4G63 into the Opel engine bay. The 4G63 is a very tall engine and the valve cover will hit the hood when it's mounted. Not to mention the width of the 16 Valve head puts the exhaust manifold and turbo right where your feet and pedals need to be, so some serious cutting and fabrication would be needed there, and plus the intake manifold will knock against the heater core area in the engine bay, so you would have to remove your heater core and cut that section of sheet metal out. But you're doing it in a Kadett, so it might be slightly different for you, I don't know.
I have a used AWD 5 speed transmission from a 1993 Eagle Talon. You might be able to use it in your project. You might be able to use the rear output shaft for your rear wheel drive and block off the front output shaft.
No, you can't. The AWD transmission has a viscous coupling in it. If you have no resistance on the front driveshaft (left open) and only the rear wheels connected to the rear driveshaft output, the VC will try desperately to transfer power to the rear shaft only but will create a ton of heat and completely fail, wrecking your transmission. Same effect as if you pulled one axle out of your rear differential and tried to drive. All of the engine's power would naturally go to the open side and it would just spin and you wouldn't move.
Anyways, I purchased a totalled 1987 Nissan 200SX Turbo in January and have stripped everything out of it. Engine, transmission, full body wiring harness, clutch cylinder, hydraulics, etc. and it's all in the process of being mounted into the GT. The 1.8 litre CA18ET is a perfect fit in the Opel's engine bay with no clearance issues (mostly thanks to the SOHC head). The transmission is on the long side and places the engine slightly forward in the engine bay, but nothing problematic. The CA18ET produces 120hp stock, which is with 4 pounds of boost non-intercooled. I have a 60-series T3 which will be fitted to it, as well as an intercooler from an '89 Starion, and I expect around 200hp @ 14psi. The CA18ET is also extremely light, much more so than the 4G63, so 200hp in a very light Opel should be a blast to drive.
I'll keep everyone updated as things progress.