One of the best kept secret in fantasy RPG history
It's E'A, by David Fitzgerald.
Supplement of new rules written in 1980 (48 pages), for combat and movement,with new character classes,spells, monsters, gods, and tables for parries, fumbles and critical hits.
Recently a copy on ebay popped up, for 200 dollars or something like that, and it disappeared in a few days, "stolen" by some crazy collector at Acaeum. Crazy in the positive sense, had i had the money at the time, i'd have grabbed that. I don't know now if i'll ever peruse those alternative rules.
Together with "Proportional combat system", it's the rarest of the rares.
About PCS, i only know that "character with a substantially shorter weapon may not attack until the longer weapon wielder has failed on a to-hit roll. if fighting more than one opponent it applies only to one of the opponents".