You are the king of your basement so if you are happy with this house rules, and your buddies are happy, then you should totally go for it, man. But I tell you, man, they are not historical correct, not even close. Special forces during WWII, like marines, paratroopers, rangers, commandoes, ninja warriors etc etc were light units, meaning they had no heavy equipment, no heavy weapons and only supply for 2 days. Their fire power were low and their combat perseverance were low too. They had to trust on surprise and luck. They were designed to make surprise attacks by sea or air to secure bridges, roads and beach heads before a main landing by the Army. They were not designed for independent operations.
IMHO, a special force unit, or SFU as you named it, should be represented by a specific plastic unit like the ones HBG are selling. It cost 4 IPC, actually in the real world it was less expensive than regular infantry because the lack of heavy equipment and weapons, but for game playability and balance most games have it cost more than infantry. An SFU used as airborne should be able to move 3 spaces from any friendly operating Air base both in combat and non combat movement. It was common to reinforce pockets with airborne troops. A transport plane did not have the range of a heavy bomber, so I figure 3 spaces is the limit. As cargo on a ship, a light unit as the SFU with no inherent supply coy with trucks and horses dont take up much space so I figure one ability of a SFU is a free ride on any surface ship. If a tranny is loaded with two land units, it still got space for an extra SFU. The SFU can even ride on a destroyer, or a cruiser, or a battleship. In combat, the idea with an SFU is it land before the rest of the army, and use its defense value in the first round of combat. An SFU attack on 1 and defend on 2 or less. But in the first round of combat it use its defense value of 2 or less to defend the beachhead. For the next rounds of combat, it join the general attack and use the standard infantry attack value of 1. I think they should move 2 spaces both in combat and non combat movement, because they had some jeeps, and usually they were good at highjacking enemy buses and trucks too. They even had bicycles, which gave them better range than slow moving Tanks.
So basically
SFU cost 4 IPC, move 2, attack 1 and defend on 2 or less. Special abilities are, they can be airborne 3 spaces when starting from an Air base, they get a free ride on any surface ship, and they have a one time surprise attack of 2 or less in the first round of combat only, no matter how they arrived the battlefield.
Another idea for a special ability is targeting during raids. I dont know how it will affect playability, but it is a fact that some special forces, like the SAS, did surprise attacks behind the enemy lines in order to target soft objects like airfields. In one case the SAS combat moved on jeeps through the desert in Libya and destroyed more that 100 German fighters in an airfield during one night, and then retreated before the German infantry could do anything. And then we have the Dieppe raid, or Lofoten raid, both by sea, where the SFU targeted specific objects. Also the German airborne attack on Eben Emael was targeting a specific fortress. Other German airborne attacks were targeting airbases in Denmark, Norway and the Netherlands.
My suggestion. A SFU also have the ability to target a specific enemy unit during a raid. This is the first round of combat only. The next turn the SFU can retreat, if this was a independent raid, or continue combat with its general values and no more special abilities if it is part of a general landing, like the Ranger attack on Point de Huc during D day, they target a Blockhouse the first day, and then continue fighting along with the rest of the army.
IMHO