should i fix my engine or replace?
 

I recently bought a 99 honada civic si with an Ls/vtec and found out the threads in the block are stripped. My mechanic told me to either get a new engine or replace the block. I wanted ask what would I need to modify if were to get a k20 or h22 engine? also, If I were to keep the ls/vtec what precautions would I need to take before rebuilding with another block. Any help is greatly appreciated thank you.
Ryan