After some checking, the CH-47 carries up to 35 fully armed soldiers (that's approx. 3 GO MMC counters, 3 SW's and 2 SMC's^) vs 26 for the Soviet MI-8 and the MI-6 is way too huge.
Armament is the typical port and starboard mounted 7.62mm machine-gun. So I would go with the 2* for machine-gun firepower, as the UH-1 fires the same 7.62mm. I would also go with a 1 on armor factor (AF). The CH-47 typically will not mount 2.75" rockets. So the ordnance and HE equivalents can be omitted. As far as troops, I lean towards PPPPP as a PPPP carries up to two squads, four SW's and two SMC's.
As for the AH-1 Cobra, I would use the same numbers as the UH-1 gunship but I would go with an AF of 2. It's AF is less than the AH-64 Apache's so an AF of 2 should be sufficient.
Hope this helps.
^ The leader counters are actually Platoon leaders and should count against the 2 SMC rule.