Broke bolt holding wire from firewall to bellhousing.
 

So Im in the process of redoing my grounds and when to take out the bolt that holds the wire onto the bellhousing which runs to the firewall. Unfortunately the bolt head snapped off, how big of an issue is it if i dont have this ground, but a 4awg ground running from the EFI harness to that same firewall location?

No biggie.
You can attach it somewhere near by.
The LIM or UIM are both suitable.

So I can run a ground from the UIM to the firewall and it will serve the same purpose as the one from the bellhousing to the firewall?

Bah, it started raining. Never gonna get this done.

If you get a chance rewire the ground with a bigger wire or even put more grounds on the car. I am not saying it to be rice but those extra grounds helps in our cars.