This may sound like a stupid question but for a set of 290 heads will both heads have 290 casting numbers or is one side 290 and the other different like 280. Thanks.

You must work in the aircraft industry, left side odd, right side even graemlins/waving.gif . In this case though, both sides are 3964290 heads, they are identical.
Jim

You were close, I was an Engineer on a Nuclear Submarine for the Navy. Port/Starboard and even/odd, old habits are hard to get rid of.

There is no right and left head per say. U can use a head on either side just flip it around, they are identical. The only difference will probably be the casting date, most arent usually the same date, but can be.