Frame Issue

[Johnny49]

Trying to find out the best way to go here. Well beyond my expertise, to say the least... I figured the gusset fix could wait, since the connection to the frame rail still seemed solid. But as I started knocking away some loose stuff on the inside, I noticed the daylight coming through. The rest of the frame is good, but with the gusset connection and leaf spring mount both being involved, it seems like this damage is in a pretty bad spot. Would certainly appreciate any advice and/or insight you guys may be able to offer...