This one is so very clever!  I managed to stack a 4 and keep the next on top, but the 4 still killed me later by being so thin and badly weighted.

As much as I like the concept, I will admit I'm not sure it's much fun as is.  It needs more depth to it, or some kind of clever twist later on.  I didn't find myself wanting to play more or go back to it.  It's for a jam, so I totally understand!  

Some ideas I had on the spot:  rotated numbers, different fonts, maybe a way to use two or more number shapes at once to get around bad placements or partial failures.  

One of the other more frustrating things with this version is that if a number falls over partway, the player is left dropping onto a slope with what feels like no chance of recovery.  

I feel like letting the player build a more complex tower that uses the whole grass platform might be a good way to overcome this, as we could get clever with leaning towers supporting each other.  It really depends on if the physics can handle that kind of abuse, however.

It really needs more audio.  Either more sound effects, or music.  Just having the sound gets a bit stale.  It's a bit odd, cause in options there is even a music toggle.  I'm guessing you just ran out of time, which is fine.  I was playing the web version, so not sure if that has anything to do with it.

Really nice job with this one, and clever use of the theme!

Neat stuff. Yeah the 4 is a bit tricky to balance, but I just discovered a solid technique:

Sevens and fours shall no longer be an issue because now the score has even more purpose. That is a 5/5 on the use of the limitation if you ask me =D.

Fun and enjoyable game. Well done.