imo Nuclear Delivery could easily be separate map from Special Delivery. It has enough content to be standalone map and it is always easier to keep smaller maps balanced. If u want to play the SD you could just play that map. Jump straight into new content of Nuclear Delivery without having to play the SD part to get there.
Map is fun indeed but has quite many choke points (That might vary on server settings and amount of players)
First tunnel is quite long. More than 10 secs of just running of Allies. That whole part could be skipped and it opens up from truck part directly to the bridge area.
I see the ND part working well as 2 stages with capturable flag bunker in middle. (That gets secured at some point when Allies advance more)
Circles 1, 2 and 3 seem to be choke points and can get hard to pass. So maybe additional tunnel near 1 (Middle bunker) so Allies have more than one way to go. (Else Axis just need to spam 1 way to stop Allies) Just made a quick possible concept on image
2 is another hard part to pass for Allies because it opens up to quite big open Area where Axis could be anywhere shooting. Similar case with 3. I The green box is a concept of some kind of wall or blockage to prevent Axis seeing both ways all the time. That might make Axis think more which way to defend than camp both entrances at the same time.