Two pieces of 10mm steel plate 50mm wide by about 250- 280mm long suitably drilled with holes to bolt to manual TA22 gb x member. I actually had to weld a threaded stud into the plate, because the box sits in an awkward position, which prevents using 2 nuts and bolts each side, to hold x member to plates.
If you want precise dimensions, your'e in luck! I will measure the assembly Tusday! PM me to jolt the memory, because somtimes I dont visit tech forum for a bit.