The easy external way to tell apart is the location of the alternator bracket lug/feed pipe.
The pumps can be used in each others blocks, the 4wd pump has MUCH more flow capacity.
The stat housing means nothing as regards the water pump as there can be a mix of 2wd and 4wd head/blocks.
Personally if it was ok I would leave it, even new ones can fail, what's worse a old working one or a new unknown one ?, as said very easy to change without disturbing belt anyway.
tabetha
tabetha