Installation of Wright R-1820-71, -60, GR1820G-202A; 702C9GC1, 2, 3, 4; 704C9GC1, 2, 3, or 4 engines and Hamilton Standard 43D50 or 33D50 constant speed propeller or Wright R1820-97 engine and H.S. 23E50 propeller, 506 gallon fiberglass hopper, wing mounted oil cooler, and revised cargo compartment in accordance with Serv-Aero Engineering, Inc. FAA sealed Master Drawing List MDL 9700 "A", dated November 24, 1980, or later FAA approved revision. FAA Approved Serv-Aero Airplane Flight Manual No. 112680, dated November 26, 1980 is required with this modification. See continuation sheets. (S2R, S/N 2526R AND UP, S2R-R3S, S/N R3S-001 AND UP) View PDF on drs.faa.gov ↗

The STC PDF is authoritative: installation instructions, ICA requirements and limitations.