/6 sitting up for several years what to do

update, I pulled the valve cover and it looks pretty rough with gunk. I tryed the tap on the valves and the rocker would not move so I pulled them and have them soaking in the parts cleaner. I also pulled to spark plugs and filled the cyclinders with some marvel mystery oil I will try to get some 5W30 tomorrow I took the radiator out and tried to turn the engine by hand with a wrench but it would not budge so I'm not sure if it is locked up or not Iwill change the oild tomorrow and see what happens.
Thanks Dan you are the \6 man Iwill keep everyone posted on what happens