Japanese to English Bus/Financial Business/Commerce (general)

This is part of an e-mail discussing changes that a supplier requested made to a part drawing (changes were requested to an automaker).

特に、デザインフリーズしてしまっているこの時期に１山目の変更はともかく、蛇腹全体の内径をφ84に変更することは、難しいと考えています。

Which of the following is he saying? (or something else)

1 Especially now after the design has been frozen, changing the first pitch is one thing, but changing the overall inside diameter of the bellows to φ84 would be difficult.

2 Especially now after the design has been frozen, it would be difficult to change the first pitch, much less the overall inside diameter of the bellows to φ84.

3. Or another translation?

I guess what I am asking is, is the meaning closer to "it's one thing to.... but it would be difficult to ...", or "it would be difficult to do..., much less..."

Thanks!