'99 engine in a '98 Mustang?

There is a '99 3.8 - 5 speed engine and trans with 40,000 miles for sale
for $500.
What are the compatibility issues involved with putting this engine in
my '98?
I don't currently have any problems with my engine. I just thought for
$500 it'd be good to have it for the future. If I kept my Mustang long
enuf I could probably use more than $500 worth of parts from it. Also,
what about storage?
I know the body style made a major change from '98 to '99. Did they
also make major engine changes?

'98 Mustang 3.8 - 5 Speed