Unless he has worled on Alfa's before I would get an Alfa place to do it. Some of them don't work out much more expensive than buying the parts alone.
You would also need to buy the correct cam-locking tools to do the job correctly, which are around £40 if your mate does the job.
the first time i did a twinspark it was the 2.0, i'd never even seen a balance shaft belt in my life, but it didnt matter. as long as you've got half an ounce of common sense, a manual and the correct tools its fine, there's no need to be a qualified mechanic.
If you're doing a one off then it's about the same price as indi garage (once you've bought all the tools). I found having a TDC tool essential.
Also 8hrs to do the first one, then it took around 3 the second time.