Hope this helps Bruce?
D16: 55mmx140mm (250ccm)
D18/D20/D21/D22: 65mmx165mm (500ccm)
D24: 70mmx165mm (570ccm)
D28 and D32: Donīt have the exact measurements, as the cladding is significantly bigger than the boiler itself.
For instance D32 is 100x230 on the outside, boiler is 80mm X 175mm but only holds approx. 1000ccm (D28 approx. 900ccm as far as i recall?).