I recently replaced the head on my 620 L20B valves, rockers, springs, etc. the whole 9 yards. when i took the old one off, i did it complete with exhaust and intake. now i am putting it back on and i kinda was wondering if it is possible to install the exhaust and intake one by one or do i need to take the head off again and do it the way it came off.(i am aware i should have done it that way now, hoping to learn but not the hard way). any help would be much appreciated.