No,just a thought.And becource it could be a total beast.A tuning company here in Denmark does a (single) turbo kit for the V6 24v with 400 bhp.
And -okay- also becource that any of the new Alfa's pleases me :The 156 is to common,and to be honest,I don't like the 147.The 166 is to big (and expensive),and GTV or Spider hasen't got room enough (and are to expensive).
And when you first got the "tuning disease",it is very hard to get rid of
A guy from my local Alfa Club was selling his Alfetta GTV to finance a 3L 24V modification to his 155 V6, I think from a 164.
If I see him again I will be sure to find out more.
When the 155 was still in production, one of the main dealers (I think they were called Daytona Motors then) sold a few 155's with 3L 12V engines (maybe 2 or 3 cars). I have seen one on the showroom floor about 1997. Don't know more, except that the sales person said it performed very well.
You can do it. It's easier if you have a 155 V6, so you can use the V6 ancillaries from the 155 to move all the thermostat housing etc, to the battery side of the engine. A GTV V6 engine or a 156 V6 engine should fit better as they all (I think) have the thermostat housing on the battery side, but the 164 and 166 is not the same. The only problem with the 2.5 24V V6 is the drive by wire thing. I wonder if that blue (UK) 145 2.5 24V has the fly by wire thingy.
I think a compromise would be an engine from a late (like '96,'97) Spider 3.0 12V. That way you can use the 155 V6 standard exhaust manifold, and I think, the thermostat etc all are in the right place.
If you have a good fabricator or you can weld yourself, I don't see a problem with any engine going in the 155. May take some work, but anything is possible.
But I think the easiest is still a Spider 3.0 V6 12V into a 155 V6. If you have a 16V, may as well turbo charge it and don't bother with the V6. Up the boost and say bye-bye to the V6ers.