Hello - it should be possible to find a (more) original engine, although you may have to settle for a 280 or 250 SE engine because they are more available than the 230 SL engine original to your car. Search for an M130 (280) or M129 (250) injection engine from a period sedan. The main difference with an SL engine would be the drive for the tachometer, but that can be fitted to the sedan engine.
Here in Europe, and also in the US, there are still a lot of sedan engines available for little money. The transportation should not be more than a few hundred dollars, so if you want to go that way, it should be possible too.
Good luck!
Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic