Static CR increase
Tighten piston to head clearance @ TDC to .035"
Larger/more carburetor area, better manifold
Split exhaust or header
Multi-angle valve job, reduced intake stem diameter to 7mm or 5/16"
Port clean up
Stronger valve springs
None of these are "linear" (produce results proportionate to expense, etc.) but cumulative: work best in combinations.
