I have downloaded a currently inactive GPL project with a view to updating it and releasing the completed codebase as open source. I'm not really a fan of GPL though and would rather licence my project under BSD.

What are my options? Is it just a case of keeping any existing non-touched code under the GPL and any updated stuff can be BSD (messy)? The source will essentially be the same codebase i.e. there is no logical separation between the two and they certainly can't be split into anything resembling different libraries.

Are my only realistic options to either GPL the whole thing or seek the original author's permission to release everthing under BSD?