I personally would pull the feeder house. 

Take out the feeder house chain and measure it's length to determine wear/life of chain.

Also there are plastic wear blocks or strips that the feeder chain rides on, on top of feeder house.

Do you need to reverse or change the top feeder house sprockets, as their job is to pull the chain up?

If the feeder house is off you might want to replace the bearing on the end of the cross auger that brings the returns over.  It would be a real job if the feeder house was on and it went out during the harvest. 

Depending on the hrs. you might need a new wear plate on the front of the feeder house.

Some one told me to use a piece of 3/8 x 3/8 x 12 inches long key stock and slide it across the concave to determine how much it is worn.  You are using the key stock as a gauge to compare the height of the concave in the middle as compared to the sides. 

Older cyl. bars are American thread, newer ones are metric.  Talking about the bolts needed to hold them on. 

I exchanged my old cyl bars with a company and wanted new bolts.  JD had to order them.