I would try oven cleaner or a product called Dawn Power Disolver, if it's still available.
I would also advise patience and repeated applications avoiding highly abrasive products and urge caution exposing the pan to high temps. That pan will warp easier than you may think. I know from personal experience--just using it on a stove top.
I have an All Clad saute pan I found in a thrift store for $7 that was in much worse condition than yours. Not only were there all sorts of burned on food residue, but it was a non stick variety that was worn through. Repeated uses of oven cleaner did eventually clean the pan down to the metal. Since it had been a coated pan though, the metal surface wasn't as smooth as a stainless finish so I used progressively finer grits of carborundum powder to smooth out the surface. I didn't have the need to go to a full polish, but I'm sure if you find it necessary, the surface could be buffed to a very smooth finish.