Dear Matt;
I just made a ring, front plate and back plate.
Diameter of the ring are 88 mm inner diameter and 107 mm, so 9.5 mm thickness.
Thickness of Front plate is 5.5 mm (2x3/32'' +GF), and that of back plate is 4.5 mm (2/32"+1/16" +GF). Diameter are both 111 mm.
Four holes in the front plate (in the picture) are for engine mount of OS GT33.
However, I can not find proper inner tube. One that I have is from a small plow trackter with a circumference of 34 cm, which just fit on the ring without stretch.
I am considering to cut the rubber, and make a tight rubber ring by overlapping two ends pasting with gorilla super glue.
Please, suggest any comment. Thanks Matt.