number plate question

Are the 79 oval backing plate the same as the 82's meaning the same size for the decal ?

Oval backing plate? In a round drum? Haha jk I believe the factory oval number plates are the same size. Can't say for sure though. I have a 79 plate but no 82 plate to measure

I think they are too, but just wanted to make sure before I order some new ones. One site says 79-82 and another says oval ?

I have another question to ask, My new number plates have arrived and just wanted to know if any one knows where exactly they go I know there are brackets for one side and the other bolts to the muffler . I seen where the one side sometimes is cut with the angle of the seat ? and some are not. should they be a certain height according to something? Even if I had the bracket the plate can be drilled any where so it's up in the air...
Any help or pics would be great. 79 wr