The mounts on the bottom of the water tank are soldered on. Very easy fix. Mine was that way when I bought it. The PO said the car always had a rattle that came out of the left side of the dash, that was it. Just get some radiator solder, flux and a torch. Super clean the areas that solder and first tin the spots they meet then put them together and solder them, very easy. After that you will be all practiced up to re solder the brackets that hold the heater core in place. Looks like your going into that direction. Lots of work but worth it. I personally would leave the water pump as my motto is " If it isn't broken don't fix it". But if you think it looks like it is old and you have the time and money why not. You may stop that oil leak by doing it. Some of the water pumps habve a lubrication spot on them, check that out. You may just want to lube it and drive the car.