1990 Engine

I feel dumb asking this but, I just bought my 16 year old brother a 1990 Toyota 4runner. It doesnt have a stock engine in it.The guy we bought it from was not sure what was in it to begin with.The mechanic we had look at it said even though it didnt have the stock engine in it that this engine looked better? The head gasket just blew today and I am trying to figure out what the original enigine was. It currently has a 6 cyl. in it. I believe its a 3.5l... Does anyone know what size engine was originally in this? Any advice? Thanks so much! -Kennidi

Curious why you wnat to know what was original?
Do you wnat to swap back to it?
Take the VIN down to a Toyota dealer and ask them to run it and see if they can pull the data for rthe truck.

Is it a Toyota engine?

Common V6 swaps are the Buick 3.8L, Chevy 4.3L, or the later Toyota 3.4L.

Stock for 1990 would have been a 2.4L 4 cyl or 3.0L V6.
Blown head gaskets is a common problem w/the 3.0.

Thank you for your replys.. great advice.. I was also wondering if we were to put in a different engine what engine would anyone recommend? Thanks again, Kennidi