combustion chamber volume: 33.5 ml (cc) 28cc
piston bowl volume: 36.5 ml (cc) i dunno seems like way too much. you are saying the piston dish is bigger that the chamber in the head. I think your chamber cc is too much as well but any experts chime in. I will calculate as flat top piston.
keep all your units metric and consistent to match 28cc:
gasket compressed thickness: 1.75 mm = 0.06809 in .75mm .075cm
gasket bore: 3.245 in 82.5mm 8.25cm
cylinder bore: 3.184 in 81mm 8.1cm
deck clearence: -0.018 (- indicates above the deck) .45mm .045cm
stroke: 3.385 86.4mm 8.64cm
max volume = swept volume + deck + gasket + chamber
(4.05 x 4.05 x pi x 8.64) + (4.05 x 4.05 x pi x -.045) + (4.05 x 4.05 x pi x .075) + 28
445.23 -2.32 + 3.86 + 28 = 474.54
min volume = deck + gasket + chamber = -2.32 + 3.86 + 28 = 29.31
ratio = max/min = 474.54/29.31 = 16.2:1
Obviously this is too high however a few cc make a big difference. So get the correct number for the piston dish and also I think the piston should be below deck but never built a JH and you will get a more accurate number.
I got the .75mm gasket thickness from Darrell Vittone years ago so I always use it in my calcs. I think your chamber cc is too much as well but any experts chime in. Thats why I used the 28cc