DO take very seriously the advice to rent a car. And more: Be aware that traffic in the entire L. A. area is beaucoup congested and slow, and you could well spend the greater part of any day just (trying) to get from Point A to Point B, even for Points A and B arbitrarily close together.
If you’re only there for 2 days, you should really plan to limit your sightseeing to several places nearby one another on Day 1, and several places nearby one another on Day 2, and that’s all.
If, for example, you try to get in Magic Mountain, Knott’s Berry Farm, Santa Monica and Malibu, Getty, and Huntington and both of those classic car museums – all in different parts of the city – there’s no way possible you could do that. You’ll just spend your whole visit sitting in traffic (which, OTOH, will truly give you the most realistic L. A. experience)!
Consider, maybe, one day visiting all those places in the Miracle Mile area (tar pits, Petersen classic car museum, Exposition Park, whatever else is there), and one day visiting in and around the Valley (classic car museum in Sylmar, maybe Magic Mountain, maybe Getty). Or one day visiting stuff in and around Hollywood (Avenue of Stars, Chinese theater with the handprints, the Hollywood sign, Griffith Park).
Just don’t try to visit too many far-flung places because it won’t work.