Nowadays You don't need to download Sfall supported ammo-mods separately.
Do this:
#1 in latest version of your sfall (extended or normal) search for a config file AmmoYAAM.ini or something similar and copy it to fallout 2 instal folder (where ddraw.dll and fallout2.exe are) and place it there.
#2 In ddraw.ini set the chosen ammo mod to YAAM. search for the option inside ddraw.ini. Save ddraw.ini after you apply the changes.
#3 that's it go play some game (although you may require to start a new game for this)