I think I got it to work. Honestly, I find the UI of the editor in KSP extremely clunky and it's really hard to find things. I used the delta core stage with the RS-68A engines and the dcss upper stage with RL10B-2 engine and put plenty of things in to SSO and GTO so far  Once, I managed to find the parts this works great. Thanks for making it! I really wish there was a mod that was better for the UI in the editor, the part search and stats layout is so ridiculously dumb. I don't know if it's possible to make a new inventory manager. I know unity, I should try it.