Look on the drivers side of the block, towards the rear...there will be a casting number...post it and we can tell you the year origin of the motor...
As far as "Do I swap them"...its your choice...
But you will need a substantial amount of parts to get this LS engine up and running....
You would also be advised to go thru the engine and make sure its all good to go...LS vs 5.7 aside...it depends on your budget and end use of the Blazer....
