Markus, I have the GoWesty 2.3 in my 89 GL 2wd. I purchased the van
with the 2.3 already installed by GoWesty. The seller had GoWesty
install the motor a year prior to wrecking it......front end crash
with no damage to any vitals, but it was totalled by the insurance co.
In short, the van came with 6250.00 of receipts from GoWesty, so,
though the front is smashed (covered with a bra) I am very happy with
it.
I live in Durango, 6500' elevation and most of my driving is higher,
in the mountains. This engine is by far the strongest VW Waterboxer
I've ever driven. It has plenty of oomph. I used it this past summer
on a couple of rafting trips and had it seriously loaded down with
equipment and, on the flats, at 5000' elevation, I found myself doing
95 (correct to 90.) It just hauls ass so I have to pay attention and
keep it down. This engine now has around 20K on it so I can't speak
about the future, but I feel very confident going anywhere in it. It
also had several things repaired by GoWesty, when they had it.
Apparently they put it through their ck list, made repairs and it came
out a very reliable ride.
I don' t know where you live, but if you are at sea level, you will be
very happy with the performance. BTW, compared to the Subie 2.2
conversion I've driven, the GoWesty 2.3 outperforms it (remember, not
talking longevity here.)
I heard, very recently, that a GoWesty 2.5 suffered a cracked piston
and that they are investigating for cause. Many believe that taking
this 2.1 to a 2.5 is going too far, and it may be, but it would help
to know how many rebuilds and what flavor, GoWesty has out there,
along with an account of how many are failing and why.
I purchased this van for 2500.00 and feel I got a great deal, but if I
was considering the GoWesty 2.3 at full price, I would be doing what
you are doing, along with putting out an APB to all GoWesty rebuild
owners for the full scoop.
Also, GoWesty was very pleasant to deal with when I contacted them to
be sure that they would transfer the warranty to me (they did,) the
new owner.

Good Luck
                    Miguel in Durango, Co.