I beat it with an A rank, though it took quite a few restarts to get it.. I suppose I should shoot for 0 lives, but getting that mid-height, far-length jump when you're coming off of a slope is really difficult.
It's interesting, sometimes activating a key will help a little, but sometimes not. I did find it quite irritating that getting the first red key would essentially kill all chances of getting the acorn.
The only thing I can really recommend is to put more random keys down BELOW, so that you can still push a troublesome platform back in position, but only at the cost of a life. Specifically, make sure the number of red keys is even, to avoid having that platform locked into a position that makes the game unplayable.
I know it sounds a bit hypocritical considering the levels I've made, but the ability to create an unbeatable scenario in this game is a major turnoff; Structurally it's very simple, even though it's quite difficult to navigate successfully, but because of that simple structure, I was left feeling like I was constantly repeating a single task. This heightened the frustration of finding out the level had fallen into an unbeatable scenario.
Hope that helps.
Currently wrapped up in: Half Life, Portal, and User Created Source Mods