I deviated a little on the transformer mounting using screws mounted from the bottom and acorn nuts on the top.
For you building a stock unit, you will place a star lockwasher on the top four holes and carefully set the end bell over them.
Slip a round #8 losckwasher over on 1-3/4" screw and place that screw in the hole nearest the safety ground.
Place three more #8 x 1/3/4" screws into the holes on each corner of the trasnformer.

Temporarily tape the screws down ove the corners of the bell end and the a lamination stack
now flip the chassis over and be careful to keep the transformer from coming out of the holes.
Slip a #8 fiber shoulder washer over each of the screws on the underside of the chassis.