Yes if you use a ETA bottom end with the flat pistons and the I head that is made for domed pistons.. I have read that it drops the compression about 1.. I have never tested so I am only going by what is on the net.
I am sure there is more data out there.

Turbo sites. There are some really fast Turboed M20 cars over in Sweden. Also Germany.- Europe. I didnt really follow these sites because I wasnt going to build a turboed m20.

You can get M50 engines cheap. You can get a whole 525 parts car for $700 if you look around. The engine will bolt up to the e30 trans.

The M50 engines go over 200k miles easy. The head gaskets can go or the head will crack. From my experiences its a 50-50 chance. RE gasket vs crack. If the fan clutches are good and the radiator good then the head should be fine. My 5 series has 214k miles and runs well. It has had the head redone. It was purchased as a blown headgasket. Turned out was a cracked head.

I just found a 525 at LKQ last week. The intake was gone. I grabbed the ECu. you can get an engine from the yard for $250. ish. Of course its a crap shoot if its good.
The swap is welding a trans bracket, shift linkage. 5 series engine mounts and trans mounts. E21 brake booster. and a very few wires need to be spliced.
Its all on the web. If you are mechanically inclined I dont think it is a huge project once you have all the parts.

A weekend to do the swap OR a weekend to bolt on a Turbo, drill and tap the oil pan. swap out injectors. Then there is the whole issue about remapping the ECU,etc. If you are running high boost fuel will need to be addressed.
I would say they are about the same time investment. And close to the same amount of $$. IF you can do them yourself.

But I have not done either. So I am only going off data.
I will be doing a m52 swap into a 318ti soon Ill let you know how that goes.

B