There have been a number of engine swaps done on 1800's over the years; I heard that a 318 c.i. V8 was installed, and there is (or was) a Ford V8 running around in Finland.

However, the only "practical" swap I know of is a B23E (non-turbo) with the CIS injection. Even this requires significant engineering as the cross-member needs to be modified, engine mounts, exhaust, and cooling system need to be fabricated or adapted to the 1800. Any engine swap will require some amount of fabrication, no matter how similar the new engine is to the original. There are no "kits" that you can buy for this purpose.

I'm in the middle of swapping a B230T into my 1800, and its a huge amount of work to make everything fit. I'm probably half way finished, and I have hundreds of hours invested already.

If your car is otherwise in decent shape, your least invasive option is to do a performance rebuild on your existing engine. I'm doing the engine swap on my 1800 as a challenge just to see if it can be done.