BASF Glysantin G48 is miscible with G05 and a bit with G40 only. It is also compatible a bit with "light silicated" new formula oldschool american IAT coolant.
If that civic was my car and was packed with rust, I would citric clean it first mildly (aluminium stuff cleans easy) to not greatly affect the corroded waterpump inside. Then refill with caltex/havoline as its easiest to get and use.
the caltex/havoline product is actually GM dexcool OAT with 2 ingredients of the recipe missing otherwise chevron would need to pay GM for the name. Its fantastic stuff to be honest but has one caveat. Unlike the japanese P-HOAT and european S-HOAT products, OAT coolant relies on keeping the entire systems walls wet for protection and that too requires about 10,000 kms of service for the antioxidants and passive additives to fully take effect.
While the other salted coolants, P-HOAT, S-HOAT work almost immediately like the old IAT stuff, they go in and coat the metal surfaces with a sacrificial layer which is replenished by the coolant itself and goes stale as it ages. This is why when you see a GM product engine disassembled the coolant passages are literally shiny squeaky clean like a brand new item, while neglected german and asian origin engines have hard deposits.
This is why when you see a leak on dexcool filled systems you see them as a black oil leak, the black is actually dust and dirt accumulating on the slick residue left behind. While on the salted coolants you see crystal formation at the leak site (bright neelum blue crystal on Honda, ruby like pink/red on Toyota and on G48 you see whitish powdered blue salt deposits, while on G05 and G40 you see white deposits like you see on a hard water faucet)