Jusrt made one for myself; it fits perfectly for my 1953 3100.
Size; make it trapezium-shaped with the long/bottom side at 130 cm's, the shorter top is 125 cm's wide and the lenght (front to back) is 105 cm's
Make sure the height of the structure is at least some 50 cm's (easier to work on)and put the wheels on the outer corners for stability.
