Fleet Snorkel conversion submarines (and some data about GUPPY conversions):
Pakistan's PNS Ghazi (1964-1971)ex SS-479 USS Diablo, Tench-class, 28 torpedoes, classified erroneously in the DB as GUPPY IIA) and Spain's SNS Almirante Garcia de los Reyes (1959-1981)(ex SS-370 USS Kraken, Balao-class, 24 torpedoes) were both Fleet Snorkel conversions.
A complete listing of Fleet Snorkel and Guppies here:
http://en.wikipedia.org/wiki/Greater_Underwater_Propulsion_Power_Program (some four years ago this Wikipedia entry was a lot shorter and less detailed, now the image of both conversions is clearer).
Some other details here (all the data also constrasted with Norman Polmar's "USS Submarines since 1945" and "Cold War Submarines"):
SNS S-31 Almirante Garcia de los Reyes:
http://perso.wanadoo.es/pfcurto/s_31.html (with sensor listing, from 1975 with the BQR-2 passive sonar of the ill-fated S-33 Narciso Monturiol in an improvised installation on the deck, as show in the last photo. Previously to 1975 probably with SS-2 (radar),WLR-3 (ESM), BLR-6 (ESM), BQS-2 (active-passive), DUUG-1 (intercept) and BQR-3 (JT in dome, passive), Ghazi probably the same sensor fit, as considered below).
http://tribune.com.pk/story/383024/warriors-of-the-waves/ (as showed in the submarine model, if accurate, it was not present a chin-mounted, or in another place, BQR-2).
In short, The Fleet Snorkel conversion were conversion of fleet boats by far cheaper, slower, noisier and with poorer sensors than the more celebrated GUPPY conversions, developed to fulfil the number of "advanced" hunter-killer submarines requested by the US Navy, impossible with the expensive Guppies. The Fleet Snorkel keep the four original fast-running electric engines not replacing them by two quieter slow-running engines, as the Guppies, and her hull and sail are not so streamlined as in the Guppies. Also, it was at least two Fleet Snorkel main variants: an US Navy variant with the big German-derivative BQR-2 chin-mounted passive 48-elements sonar array (developed from the German Balkon-48), and other diverse austere variants for export, mainly for training submarine crews and employ the Fleet Snorkels as targets in ASW exercises in many allied navies, with simpler sensors, usually the BQR-3 passive sonar, an old wartime JT in a dome. And another main difference between Fleet Snorkel conversions is in a Tench-class Fleet Snorkel converted her torpedo capacity was 28 (as Ghazi case), not 24 as in the Gato and Balao-classes conversions (as Almirante Garcia de los Reyes case).
About the differences in maximum speeds,from many sources (test depth in all types 400 feet/122 meters,except some austere Fleet Snorkel and Guppy IB converted from Gato-class, 300 feet/90 meters):
Fleet Snorkel: surfaced 18 knots, submerged 8,75-10 knots.
Guppy I: surfaced 18 knots, submerged 18 knots.
Guppy IA/IB: surfaced 17 knots, submerged 15 knots.
Guppy II: surfaced 18 knots, submerged 17 knots.
Guppy IIA: surfaced 17 knots, submerged 14,1 knots.
Guppy III (all the nine boats conversion of Guppy II): surfaced 17 knots, submerged 15 knots. Capables of use Mk45 ASTOR nuclear torpedo, and with passive BQG-4 PUFFS (intercept) added.
As stated previously, 24 or 28 x 21” Torpedoes (Depending on whether Balao or Tench was converted).
Guppy IA conversions from SS-475 Tench class (originally 10 in tubes +18 reloads): 10+16 reloads = 26 total torpedoes.
Guppy IA conversions from Balao class (originally 10+14): 10+12 reloads = 22 total torpedoes.
Guppy II (and probably Guppy III) conversions from SS-313 Balao/Perch class (originally 10+14)
and SS-381 Balao/Sand Lance class (originally 10+14): 10+12 reloads = 22 total torpedoes.
Guppy II (and probably Guppy III) conversions from SS-475 Tench class (originally 10+18): 10+15 reloads = 25 total torpedoes.