After lots of consideration I have changed my drivetrain plans.
Currently my Deon is sporting a Cologne V6 & IB 5 gearbox. This was always bound to be thrown out in favour of a more modern engine (they don't call it the "iron pig" for nothing).
I thought long and hard about an Alfa V6 3.2L 24V, as well as a Jaguar V6 3.0L 24V. Both deliver about 240 HP stock and have aluminum engine blocks. However, when I measured up the engine bay, things became a lot less straightforward. Both engines may fit with some effort, but positioning is far from ideal due to lack of space. Below you can see both engines in the the engine bay:
The Alfa V6 is sitting too high and too far back, placing the driveshafts in an awkward angle, which is not ideal.
The Jaguar V6 is even bulkier, it is sitting at the right height, but too far back, giving the same the driveshaft problems.
Apart from the driveshaft problems, I would prefer to have the drivetrain center of gravity more forward, to improve handling. Furthermore, if I decide to turbocharge the engine, which is likely, one will have increased space issues AND the front turbocharger will heat up the cabin.
Enter the VW VR6 24V:
You can see that it can be positioned more to the front, giving straight driveshaft angles and moving the center of gravity forward as well.
The VR6 is compact and available from 2.8 to 3.6L, 204 to 300 HP stock. It is not a very sporty engine, it is quite undersquare and the internals are quite heavy. I hope to find a 3.6L version, giving between 260 and 280 HP and less undersquare. Lighter flywheel will hopefully make it more lively too.
On the plus side, it is very tolerant to turbocharging. As for turbos, the exhaust is at the back, where there is a ample space to place turbos, cats and exhaust, and lots of air around them to get rid of the heat. Due to the Max Power brigade turboing their Golf VR6's, there is a lot of experience and parts available in this department. I am thinking 400 to 450 HP in a twin turbo setup, to keep engine response and drivability as good as possible. This can be done without enhancing engine internals.
See below for a 3D pic of the setup: