replaced. Just realize a small bit of coolant will be lost so check the radiator every so often if the replacement will take a while to get installed. Realize cars back before the mid-70's never had those tanks -- we all survived (LOL).
Not a big deal to replacing that tank - driver side wheel off, remove front wheel well liner - replace tank.
Pretty sure the lower shroud is important for good air flow - so not a great idea to leave it off. You might be able to snap it into place from the top - never tried tho....