Thank you very much for the comments, guys!
And yes, it took quite an effort to collect and systematize all the pictures and documents; but since I'm very happy with the result I'd say it was worth it.
Here are two more Stalwart modifications. Three ships of this class were used in counter-drug operations known as "War on Drugs" between 1993 and 2002 under Joint Interagency Task Force - East. The SURTASS equipment was removed and long range radars were fitted: SPS-49 on Stalwart and Indomitable, SPS-40 on Capable.
(I'll update the first page with these drawings as well)