That dish looks like my 1 meter Prodelin. Here are some pics of the lnb bracket and such.
The dish came with a manual: 4096-433 Assembly Manual for Small Aperture Ku-Band Rx/O Antenna System, Rev B. 1997. I think that's the part number for the small aperture mount for the 0.6 through 1.0 meter dishes...
Part numbers for the bracket are:
4080-060 Top Feed Clamp
4080-059 Feed Mounting Bracket
FWIW.
If that plastic bracket doesn't work out you might get
this prime focus adapter from Sadoun, stick it in a vise, bend it as necessary, and drill a couple of 1/4" holes for the arms if necessary. YMMV
EDIT: BTW, the feed mouth is about 27" - 27.5" from the face of the dish as measured from a point halfway between the side arm mounting points...