1998 4.3L Blazer Engine to a 2004 Blazer
 

My 04 Blazer's transmission is going/went. Doing some research online brings me to the realization that my two immediate options are a full rebuild or a replacement.

My uncle has a 98 Blazer with a rusted frame that I can have for cheap. The trans was recently rebuilt and the engine runs fine. I've read that a 98 transmission probably won't work with my 2004.

This brings up my new question. Will I be able to (easily) swap the engine from the 98 into my 04?

2004 doesn't have EGR and machining on block for knock sensor is different. Swap intake/exhaust manifolds from 2004 and deal with knock sensor mounting and it should work. How to deal with knock sensor will have to come from someone else.