Question:
"I'm replacing my front wheel bearings on my 78 leyland. (drum brakes) I fitted the new bearings and seals and went to fit in the drive flange and i noticed the seal is too big to seal on the flange. Is there a sleeve or spacer that the seal seals on?"

Answer:
"Yes there is a tapered collar that sits between the flange and the bearing.  You must have set them aside when cleaning things up!"  See Photos Below