You should be able to get by with some primer-surfacer and sanding to fill these areas. There is no previous collision damaged to be repaired on this piece. This is guaranteed to be a real-deal factory heavy-duty piece, NOT one that somebody welded a tab onto. It goes without saying that these are extremely tough to find in any condition.
When only real parts will do for your restoration. The item "1970 Chevelle LS6 OEM Radiator Core Support Heavy Duty Cooling withTab V01 4-Core" is in sale since Sunday, October 3, 2021. This item is in the category "eBay Motors\Parts & Accessories\Vintage Car & Truck Parts\Cooling System".The seller is "malibu_400" and is located in Ridgefield, Washington. This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, China, Sweden, South Korea, Indonesia, Taiwan, South africa, Thailand, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Bahamas, Mexico, New Zealand, Singapore, Switzerland, Norway, Saudi arabia, Ukraine, United arab emirates, Qatar, Kuwait, Bahrain, Croatia, Malaysia, Barbados, Bangladesh, Bermuda, Brunei darussalam, Bolivia, Egypt, French guiana, Guernsey, Gibraltar, Guadeloupe, Iceland, Jersey, Jordan, Cambodia, Cayman islands, Liechtenstein, Sri lanka, Luxembourg, Monaco, Macao, Martinique, Maldives, Nicaragua, Oman, Pakistan, Paraguay, Reunion, Uruguay.