rebarlee

i have twin omc king cobras - 7.5L Fords
I just had a valve job done and .0001 milled on heads.
Engine was hydro locked and bent pushrods. After installing new exhaust manifolds and risers installed what i thought to be correct pushrods and valves would not close. Now I'm told that there are 8 listing fopr pushrod lengths for this engine. How can I determine which is correct length?
Serial number? Engines is a 1990 model.