Hi Im going to change the 350 head with 305 head to increase compression ratio . The combustion chamber on 350 head is 76cc Which casting number and 305 head spec will be good for my application ? Do I need to use double spring for valves ? How I can modify ports ? Pistons are 0.030 dish . Following camshaft , intake and carb will be install on the engine : http://www.summitracing.com/parts/edl-1411 http://www.summitracing.com/parts/edl-7101 http://www.summitracing.com/parts/edl-7102 Please give me advise for 305 head choice .