Strange S60 Rear End Help
If you have a weldor with a modicum of experience, they won't warp it by putting the perches on. I have welded perches onto a handful of 8 3/4 housings which are relatively thin stamped steel with no issues. My S-60 was fine after my welding job on the perches.
Remember, the S60 is not a 1 piece, stamped steel housing like the 8 3/4. It has thicker axle tubes that are pressed and welded into the iron center casting. It is all very strong - and I think you will be fine.