I think that I have a good idea of what the US force will have available for Plan Rubber, plus a couple of additions.
During March 1942, all of the above ships, excluding the battleships, were formed as TG22.7 for a brief time, patrolling the Caribbean and Atlantic near Bermuda. The battleships were being used as convoy escorts. shuttling back and forth from Maine to Iceland. This, I feel, is a good basis for my Plan Rubber US force.
Additional forces could be drawn from the following:
CA Tuscaloosa - assigned to the US Atlantic fleet, she spent much time operating with the Royal Navy as a convoy escort. As USS Augusta is a thin-skinned Northampton-class heavy cruiser, the better balanced New Orleans-class Tuscaloosa would be a good option.
DD Rowan and DD Hobson - these two destroyers were just coming off time in the yards for refitting and could be available for escort duties.
CVE Long Island - the first US escort carrier, USS Long Island spent much time as a plane ferry later in the war. For Plan Rubber, I envision her with a small deck-load of USAAC P-40 fighters to be flown off for use at a captured Brazilian airfield, and her normal naval aviation complement - stored on her hangar deck - would be available afterward. She would be very vulnerable prior to the flying-off, but there is a lot of potential with more US aircraft in the air.