This is the start to finish of the replacement of this gas valve replacement, along with a burner assembly. You will have to rework the gas line into this to make it work, no way around it.
Make sure your gas line from the burner is super tight into the gas valve, and be extremely careful you don't cross thread it. I tightened it really tight and still leaked a little gas; went and tightened it up till it stopped leaking.
The valve on your RHEEM water heater is no longer made. The one I installed is the new retrofit model, and you'll have one 3 pin line not in use when you install this new valve. Make sure you set the gas valve to 120 degrees AFTER initial firing of the gas thermostat.