????????

I see no dowel pin on the top sheeting. If you are talking about the cut line above F3, that is simply a butt joint because MK did not make the top sheet one long piece, it was a rectangular piece mated to a tapered one. There is no top hatch.

As I look at the plans, MK also changed the belly hatch. On mine, H3 and H4 had a 30 degree slope down to the rear from the TE, which makes it easier to fit vs the squared off hatch in the plans.

Oh, I wish I could find my original.