You or someone you trust has to be able to make that call. Unless the engine is clearly toast -- there's a hole in the block for instance -- the engine will probably have to come out of the car and be subjected to some degree of tear down to determine its suitability for a rebuild.
An experienced tech can drop the engine in under a day (8 hours), easy and based on what I've seen here and there in probably about half that time.
You are not on a clock, though, and can take your time. In fact I would advise you to take your time. Document -- photograph -- every hose every connection, in short everything. (This really is important. For example I was taught that if in the case of a car like a Boxster had to have its half shafts removed to drop the engine one has to mark the half shaft flanges so when bolting these back to the tranny again they end up the same exact place as before. If not the car may have a very hard to diagnose and correct vibration that feels like it is tire or wheel related but is of course related to the half shafts being installed differently than before.)
To repeat: Document (photograph) everything.You will not remember where everything goes months later. And months later it will not be obvious where everything goes.
Another way of putting it is getting the engine out is far easier than getting it back in again, with no drama and with the result the engine fires up the first time and develops no issues from the installation (or the rebuild for that matter).
As tonyd suggests do a search. There are I'm sure -- I've viewed a few at least part way through -- videos or an album of photos of Boxster engine R&R's, and even a few documenting the rebuild process.
If the engine needs rebuilding you might be better off dropping it and shipping it off to a well-known/reputable engine rebuilder. These are not that complicated of an engine but Porsche has not published clearances/tolerances as far as I know and I've tried to put my hands on this info.There are a few rebuilders who have learned what they need to know in order to arrive at a successful engine rebuild. They are not cheap rebuilds though.
Now this is not to say an amateur can't successfully "rebuild" one of these engines. He can provided the engine doesn't need much in the way of rebuilding. That is to say for example I came across a 996 engine -- at a Porsche dealership -- torn down for repairs for a failed IMS bearing. While the rebuild was done by a very experienced Porsche tech, all the rebuild consisted of was after a through cleaning a new IMS and bearing, probably an oil pump, a couple of chain tensioner rails/guides and new gaskets and supplies.
The tech found the rest of the engine just fine. (The engine only had around 20K miles on it and since there was nothing reportedly wrong with the engine other than the failed IMSB I suspect the tech as per Porsche didn't bother to really check every bearing with a micrometer but I'm sure did give every one a visual check looking for signs of excessive wear.)
If you find the crank mains or rod journals worn this can be a real problem. There are no oversized bearings available so one can't regrind the crank undersized and fit oversized bearings. There are no aftermarket cranks AFAIK and a new factory crank is very expensive. The original crank even if not worn should be checked for cracks. Not too many months ago at least one Porsche engine builder was soliciting for used engines to replenish his stock of cranks.
Anyhow, search out the engine removal and installation videos. View them all. Create your own manual on how to do this. Know it backwards and forwards. (When I prepared for my first solo engine R&R I knew the process by heart, memorized it by absorbing all I could get my hands on on this subject for both specifically my car and its engine but for engine drops and rebuilds in general.) Before you drop the engine though search out and view all the engine rebuild stories, videos and photo essays to see if you want to tackle this.