Either you missed an intake bolt to the head, or one of the TWO support brackets from underneith.

Also, you didn't identify what year 300E. If it is the M104 motor, then yes, replace the timing chain if you are doing the head gasket, as well as the timing chain guides and tensioner.

If it is a M103 motor, I'd personally hold off on the timing chain for a couple of reasons. 1) it is really easy by the factory procedure to replace the chain with the head and camshaft installed on the motor by pressing out a chain link rivet on one of the links, linking the replacement chain to the old chain, then while rotating the motor by hand with a socket on the crankshaft using the old chain to draw the new chain onto the sprockets. 2) the timing chain on the M103 is comparetively short and a pretty straight run, only travelling around the camshaft sprocket, the crankshaft sprocket, and the tensioner. As such, it really doesn't wear fast at all.

On my motor (M103 with 78K miles) when I recently replaced the headgasket, I didn't replace the timing chain, but I did replace the tensioner rail and guide rail, just because they are plastic and do wear and get brittle with heat and age.

If you do pull the head, as a minimum you want to replace the valve oil seals, check the valve guides for wear, check the head surface for warpage, and re-lap the valve seats.

good luck

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