The actual bellows dimensions:
Front (external) 130mm square
Rear (external) 145mm square
Bellows pleats measure about 12mm so subtract 24mm to give internal dimensions
Collapsed, the bellows take up about 25mm. Extended, they are about 200mm long but will stretch to about 270mm.
(they have been cut down from a longer set from a monorail camera).
The hole in the plastic plate to the front is 86mm diameter. The plate is 139mm square
There is a similar rear plate the same size with a 124mm square aperure which is fixed to an extra plate which I made which is 168mm square.
It's probably easier for you to remove the bellows from the plates and make your own adaptor.
Anyway, if they are of use to you, send me your address by PM and I will post them.