Thanks everyone for the comments. I will use the LSAT Powerscore RC book. I'm not going to read everything, but I will try all the exercises and read the answers. I've read a little bit of this book and so far:
1. Yes, they assume you can mark up the test since LSAT is paper/pencil. It looks like they even devote a whole chapter to how you should mark up each RC passage.
2. Many of the RC passages deal with law-related material, whereas GMAT doesn't have any of that. LSAT passages use law, science, social/humanities topics, and economics topics. So most of the passages are relevant except for the law-specific ones.
3. The main advantage I see in using this book vs. 1000RC is there are answer explanations and you know that the answers in the book are correct. I will supplement with 1000RC/GmatClub explanations as well.
I won't be getting the
MGMAT RC or Powerscore RC (for GMAT) as my RC is already ok and now I have this book. I may use the Logical Reasoning Bible sparingly since I've already finished the Powerscore CR Bible (for GMAT).