Change timing gears without loosening or pulling the oil pan?

Haha. Your slant will NEVER perform like a Tesla.

If it was me I'd just pull the engine. I can't see getting a good seal again on the timing cover if leaving the pan installed. It would be awkward as hell to degree the new timing set too. One of the gurus might have tricks to do this but to me it looks like an exercise in frustration to do it in-frame.

If you do this get a Rollmaster timing set. Spendy but well worth it.