Carl's contribution as "Mixdown Producer" was enough to give the album that polish we all admire (the mixing process can radically change the way tracks sound, in this case much for the better, I'm told). I doubt he did any arranging. Some of the guitar is him, some is Ed Carter, some is probably Billy Hinsche.
I'm probably missing something obvious, but please explain this to me as you would to a 5 year old. I get that mixes can make a difference, as in the 15BO vs MIU mixes of Peggy Sue (i think), where the instrumentation balance is changed. But it doesn't seem to me like there's much to bury in Love You. Is it just a case of Carl adding overdubs? If not, then what? Thanks!
Look at this way - have you got the SOT Smile? Those are straight off the tapes, all the faders up, with no mixing of any kind done to it. Now compare those to TSS. You can radically change things in mixing via effects (such as EQ, compression) or just moving the instruments and vocals around. It's not so much the arranging side.
I should try and find the Love You outtakes in my highly disorganised iTunes. IIRC, they are hardly the crispest quality, so a comparison was difficult.