It will gunk up pretty fast after the swap if you didnt get it all out. And you will notice it pretty fast. I have found the best coolant to use in any application is Acuras Blue coolant. It keeps LS1 cars 20 degrees cooler.
I would assume that there are things your parents still dont know to this day about you? I know there are many things that I did for a very long time (over a year) and my parents to this day dont know about them.
That sucks. Looks like the majority of the damage stayed in the front clip. I feel for that guy. That car took a lot of work all to be fucked up by some ass.