200K on a Trooper? Well, if your head gaskets aren't shot, they will be,
from the people I know who own them.
I'd replace it with a rebuilt from a "reliable" source. Note "reliable".

Check the Yellow Pages for a Japanese engine specialist that sells JDM
engines. These are relatively low-mileage 'pulls' from Japan. They
should be able to source a later engine with more power, and install it
for a reasonable price.

I've gone the rebuilt route and it is a really huge gamble.  I don't
regret it - but I managed to win.  If you win, this route is a really
good way to get an excellent quality car for really cheap.  But be
aware that it's high reward, but high risk too.  There's no free
lunch.

For starters, for your Trooper to even be a candidate the following
MUST be true:

1) Immaculate interior and exterior, glossy paint, no rust, no accidents,
no bent fenders, etc. etc.

2) Suspension, wheels, tires, etc. still in good shape.

3) Transmission still in good shape.  If it's never been rebuilt in the
history of the vehicle, assume that it will be during the life of the
new engine.

4) You must have at LEAST $5K in the bank, or accessible via
credit.  Not that your going to spend this much - but you need it
just in case.

5) You must be intending to own this car at least another 10
years.  These kinds of cars have NO resale value beyond book
value - if a buyer has enough money to pay for a 2-3 year old
rebuilt engine, he has enough money to buy a junker with a
blown engine and get a brand new rebuild.

There are people who get tired of staring at the same interior
of a car for 20 years.  Make sure your not one of them.

6) You must be willing to self-insure.  What I mean here is not
liability but property.  Your insurance company is going to regard
this vehicle as a 10 year old 200K mile car with a book value of
basically nothing.  You are going to regard this car as a 10 year old
0 mile car with a book value of $3-4K.  Thus, any kind of
comprehensive insurance you are carrying on this vehicle will be
worthless.

A friend of mine had at one time a Geo which he loved, and
which met criteria 1-4.  His engine blew.  Against my advice
he went the rebuilt engine route.  6 months later he rear-ended
a semi truck and the car was totaled.  He was -extremely-
lucky though, his car insurance was though Grange and he
has had the same insurance agent all his life, never had an
accident before, and the agent
arrainged for the book value of the car to be inflated enough
to cover his cost on the engine.  He ended up with enough
money to pay for his cost on the engine - so he was even
after a fashion, and the insurance company sold the engine
(and probably took a loss on the deal, but as they had
more than made it up previously I think they counted it
off as goodwill)

If you still want to go for it, then say so and I'll post some
advice on how to go about getting a good rebuild in the vehicle.

Ted