I apparently have 2 tubes cracke on the inside and cant get the tig torch in there deep enough. Has anyone ever cut the outside tube off in pieces, welded the inside tube and then welded the outside back on?

Sure have
Not on stellings, but on the old Kiekaefer headers (circa 1980). Did it almost every weekend when they got older. Make sure to fill the pipe with nitrogen or argon to protect the back side of the weld.

yes,,weld the crack up with ''317ss '' rod,thats what stelling...when done welding grind smooth and then weld a 316 ss patch over the area..after your done repairing the cracks i will take a piece of 316 ss and weld a inner lip around the hole so when i weld on the piece i cut out to access the crack has a step so it dont fall into the hole i cut out..then i start with 320 emery and worn my way up to 1000 then polish..also blow some argon inside the tube your welding so the bead your welding wont slag up on the inside of the header tube..