I used both stock 273 cylinder heads and stock 340 cylinder heads on my .060 over 273 block bracket racer. With the 340 heads (2.02 intake) I notched the cylinder block for clearance.
Best time with 273 cylinder heads was 12.72, but with the 340 cylinder heads my best was low 13's. I believe using the same 273 domed pistons with both cylinder heads predicated a loss of compression (and performance decrease) with the 340 heads. At the time, I was young and ignorant and wasn't knowledgeable about CC'ing methods, etc.