Check my work-Chime in please

Yeah that does it . the math says 273.29 cid
I knew that . I just forgot it. Sheesh!

How did I get the 2.439 pop-up? Well at your bore size the 1/2 inch down fill volume should be 86.439cc. Since you were only able to get 84cc in there, your piston is too big and therefore must be a pop-up; equal to the difference.