Yes an ej257 bottom end will work with 05 LGT ej255 heads. There are differences between the blocks depending in what year you land on.
You should read through the engine FAQ here as well. I'm sure it would be helpful.
Last I checked flatironstunning had a new OE block priced at $1800 plus shipping...
Depending on what failed you will likely want to replace a few other items though...define "blew up" please.