Not impossible to do it in 3 days with everything lined up (which will require more than 3 days to coordinate and source), but Murphy's Law will show you who's King!!
Realistically speaking and not being a Debbie downer, it will be hard to get it done in 3 days. (Everything would have to be ready before you get the spot)
You have to source all the parts, make sure the engine you're getting has all sensors, the harness is clean and make sure all is complete. If you plan on getting maintenance parts for the engine, you have to wait for those and to make sure everything fits, you have to do some work there as well.
*Keep your ST165/ST185 mounts intact. Transfer them onto the ST215.
*There are a few experienced guys that do harness work. It may take you a week or so to get the harness back to have a plug and play affair. (Depending on their workload). You won't need an aftermarket EMS. Check out Wiregap or Dr. Tweak. Email them and decide who you would prefer working with. That will simplify your swap.
*If you have an ST165, you'll have to find a way to relocate your intercooler or cut your hood (unless tastefully done, try not to
)
*ST185, you'll be ok with the top mount unless you want to go FMIC
*The ST215 has a decent bolt-on aftermarket. (shop around. Some shops carry a good amount of parts for the ST215)
You'll enjoy the engine once in. But plan wisely if you only have 3 days to get it all done. Best of luck!