Quick question, How hard would it be to put a Uno turbo engine in a Fiat 127?

Getting hold of an Uno Turbo engine these days is probably going to be the most difficult part. Unless you desparately want to maintain the period 'purity' of the 127, you'd probably find it easier to obtain a modern 1.4 TJet engine. In terms of difficulty of installation they're likely on an equal plane requiring custom mounts, exhausts, etc. The TJet will have the advantage of being more reliable, more powerful and having a lot larger spares pool to draw from.