I was concerned that the down-gauge of EZE to budget-configuration 777 would have this effect on redemption availability ex-EZE, as in my last few years the only redemption seats have always been in F (and sometimes hard to find).

An option to consider is to book into F on the good old 246/247 from GRU, which I recently learned has the benefit of no fuel penalty if booked ex-Brazil. A recent look showed good availability on that route, which doesn't surprise, as it's now the same equipment as before, with no through traffic. If a short stop in GRU is not a problem for you, then the savings on fuel penalties could cover a paid fare from AEP or EZE to GRU.

Good luck, and welcome to FT!