should i worry about vibrations?

 

Hard to tell from the pic but if it's raised up from the wheel mounting plane the wheel won't seat perfectly flat & true, so it could cause issues. Guess you won't know until you try.

 

I guess I could put a piece of wood or something and hammer it smothe?

 

The flatter you get it the better. There shouldn't be much vibration since the weight will still be in the proper place/proportion or at least enough for the spacer. As blnewt stated, it's the seating surface that is the most concern. I would prefer some discrete hammering over machining so that you keep the same amount of mass/weight.

 

thx guys