I am not sure a 1/2 aluminum plate will give a "better"seal. I have never seen a water pump leak there yet.
However, since you're removing the front cover to replace the seal, now is the time to really inspect or replace the timing chain. A quick pretest is to remove the distributor cap, roll the motor over by hand with a breaker bar to TDC. Now watch the rotor carefully and move the crankshaft the opposite way. Stop the moment the rotor moves. Now look at the timing marks. If the crankshaft moved 10 degrees or more the timing chain needs replacing. Hope this helps.