What is all needed exactly to swap a 4l80e into a 3rd gen Fbody? Will there need to be modifications to the floor pan? Thanks

 

A 4l80e will fit with little modification to the trans tunnel. Your biggest issue will be the transmission cross member, for no company currently makes one to fit the 4l80 that I know of. Search and you will find multiple threads of people detailing how they made one

 

I did it, and as jpearcy mentions you'll have to fab up a crossmember , figure out a torque arm mount and probably shorten your Torque Arm.
Depending on headers or Y-pipe you'll get creative with exhaust too. It all fits, be it snug for sure.

I've read that the factory shifter doesn't work with the 4L80 but I didn't read that until I got mine to work just fine with it. I did use linkage parts from a 700r and the 4L80e to get the "sweep" of the selector right, but it works fine.

 

So other than crossmember, torque arm mount, and floor pan i should be good? Will the stock driveshaft work with the 4l80e? Or would i need a new one? Thanks

 

No, it'll be too long because the 4L80 is longer over all. Have one built with the bigger yoke anyway or for use with a conversion U-joint.

 

And because my Crossmember was further back I ended up modifying the tails of the sub frame to use an extra mounting point on each side.

there is some discussion as to the increased leverage it puts on the subframe so I added a wing tabs(?) to use the forward most factory mounting point.

 

Hooker sells a new "Black Heart" set up that includes their LS swap motor mounts and their LS swap trans mount. They have an adapter for the 4L80.