Putting back together 4.3L Vortec 0L082849 and having an issue with valves remaining open. I'm torquing the rockers down to 16lbs as per the manual. This block did not originally have these heads...the heads are off a 2001 block. Seemingly, the push rods are too long as I am using the originals, but I don't see a difference in the part numbers between the years. Any thoughts?