If anyone by chance doesn't know where to find the old level editor, here's the internet archive upload of v4.3: https://archive.org/download/pizzatowerdemobuildspublic/Patreon/Level%20Editor%2...
You should probably know where to get this (or just have it) when you get here, but I wanted to make this comment incase.
Also, any version of the level editor works, as long as it's a mod supports v4.3 and above. PTO's level loader also works.