Mike,
upper rails must be 1.5" to the mid plate (2" ahead of it to be specific), kidney bars and rear cross member, rear end upright wall thickness, lower frame rail diameter behind rear end uprights, pinion cross member wall thickness, seat brace diameter, rear end bay diagonals, side bay upright and diagonal diameter/wall thickness. There are also some criteria for the tubing in the bay ahead of the rear end uprights depending on the rear end mounting version used.
Roo
