I decided to give the most recent version of this scenario a try. My observations are similar to those of McMonkey from earlier this year. I'm now at the beginning of 1951, and Pusan and most of historic South Korea is firmly in my possession. The initial AI offensive from North Korea was conducted well. However, it was a little too easy to defend Pusan from the attacking hordes after the 2nd turn. UN reinforcements are a bit too strong, especially the technology-driven "Reinforcements 1". (I have no idea if subsequent reinforcements are appropriately balanced, as I haven't gotten that far yet.) As others have mentioned, the attack/defense stats of air units are too strong. (BTW, what does the P-82 Twin Mustang do?) My Sea Fury aircraft are always the first units to defend whenever North Korean ground units attack Pusan. I would suggest that you reduce the defense values of air units and give them the "x2 on defense versus air" flag.
I also noticed that some of the TOTPP parameters may not not have been implemented correctly. The defense bonuses in @COSMIC2 look wonky. FortifyDefense and FortressDefense values are both specified as "1". This effectively halves the defense strength of ground units (50% penalty) unless they happen to be situated in cities and coincidentally not fortified. I suppose you didn't intend to handicap units that are fortified. Were you instead trying to remove the defense bonuses of forts and fortification altogether? If so, the values need to be specified as "2".