So I think we've established that the Admirals would be suitable for conversion now onto more specific questions about plane numbers and how they'd stack up as ships against the Lexingtons?
With the RN devotion to the Armored flight deck and fully enclosed hangers, along with the second flight deck that the RN and IJN tried?
Figure 50-60 aircraft in the 1920's, down to mid 40s by WW II. As a comparison the
Lexington was rated for 120 aircraft, although she rarely carried more than 90, even in the early days (
Akagi, which shared the RN 2nd flight deck design, carried 60 aircraft +25 or so disassembled in a lower hold).
USN doctrine was to max out the size of each air wing to the size of the carrier, something that was facilitated by the use of squadrons that were not necessarily wed to a particular ship (as an example, on 12/7/41
Ranger had VF-5 on board instead of "her" VF-4 since VF-4 was transitioning to the F4F). IJN practice was to keep air groups together and have the same group assigned to a ship. This turned around and bit the IJN a couple times during the early part of the war.
As far as how they would stack up, it all comes down to the aircraft and weapons the planes had available. I would take a late war
Independence with her 34 aircraft (TBF and F6F or F4U) and her 5"/38 AAA over a 1939
Lexington with 90 SB2U, TBD and F3F with her 8"/55 MK 9 guns and 5"/25 AAA. Unfortunately the FAA tended to suffer in the aircraft department, although an ATL FAA would doubtless do far better.