Having the US or UK get to SZ 127 sounds awesome, but the problem is that from SZ 91 you’re hitting Norway from SZ 112, which is an exceptionally bad place for the allies to be (no air base) and its also 3 spaces to SZ 127 with no port to use. That means that US 6 is too early, and that US 7 would be your first chance.
I may be wrong, but you also really can’t effectively use the transports the way you describe. If the transports have to move (rather than sit in SZ 110 and just bridge), it takes ridiculous logistics and time to move any troops. UK goes before the US, meaning that if the transports are empty, the UK can load (then move on US turn) then unload and attack on the subsequent turn but you cant repeat this maneuver, its one shot (because the transports are no longer next to the UK on the UK’s turn) and America cant use them while you are.
Worse, only the UK would be amphibing, and during the offense, the US units would sit idle. If Germany has a single fighter, it can scramble out over your invasion fleet (without an airbase) and none of the US warships can do anything about it. (Could be wrong here, but I think that’s what the FAQ says) With only UK fighters to help, range becomes an issue.
Showing up behind German flanks with a huge big stack of US units sound awesome, but it takes patience (US does nothing to stop the Axis for 7 turns) and I’m not that certain that you can stymy Germany with a single wave before it takes Moscow or everything around it.