The only thing that comes to mind that would damage the engine would be if it were to not have oil pressure when it started. Since you have the valve cover off, I would start it up with the cover off, watch to see that all the rockers drip oil, then check the valve lash.
And since the gas tank is off... Have you looked inside for rust? Good assumption it will be rusty if it's original and been stored outside.
Providing the engine is good, the transmission will need to be drained and flushed. Notorious for collecting water. It gets in around the shifter boots and the upper three point mount boot.