Just adding my 2p worth here, Basically the thema turbo engine is the same as the Q4/grale block, there are diffenences however with the ancillaries, makes sense really, on a grale the alternator is hidden away but on a Q4 its easily accessable. If you think about this logically why would Lancia/Alfa who weren't in the best of financial states back then bother to design another 2.0L 16v Turbo engine when they already had a cracking one sitting on the shelf. Making it fit could be fun, and not something that I would look forward to. Something else sticks in my mind about the thema Lump, and I may be wrong on this one, but doesn't it have larger exhaust valves than inlet? Something to do with improving torque. On the subject of torque curves, even though the EvoII and Q4 have almost identical engines the Evo makes 15bhp more, all to do with making the engine in the Q4 more economical, with better midrange.
BUT if this post is all to do with slotting a thema turbo engine into a 155, I would say that you are probably making work for yourself, the best way to go would be to get yourself a Dedra Turbo (about 25p is the going rate) and swap the complete engine/gearbox out of it. The advantage of this route is that the Dedra and 155 are almost identical. If you don't believe me go and sit in one, you will feel right at home. As it is tuned in the Dedra it makes 165 bhp (already 15 up on your 2.0L 155) But with relatively few mods you could coax that engine to produce 250bhp with more torque than you can ever want. And after all if it goes bang, just go out and get yourself another Dedra.
So there you go. Just my ideas on the subject