Rusty Frame Sectioning

My '89 XJ has frame rail rot starting at the driver side rear - leaf spring
plate to frame rail and extending half way up the kick up...

The area is mostly the bottom of the rail - but overall rail quality there is a mess.

I'm tempted to have the salvage yard whack a salvage rail from before the plate extending to clean metal.

How much of what should I specify & should this be butt welded or overlapped to the existing frame rail ?

"In the Weeds":dunce: :wow: :us:

Id use atleast 1/8 and over lap as much as possible with as much weld area as possible to rebuild the frame rails after cutting out the cancer but thats my opinon