The meaning of なんだって here


> 指名して誘うんなら、お前じゃなきゃダメなんだってくらいの熱意は見せないと失礼だ

So it's like

> If it's a designated nomination then you're the one who has to go. After all
> it would be pretty rude if you wouldn't show off your enthusiasm.

So くらい is like a comparison which is like an extent but in this case how does
that work with なんだって?




You got the translation wrong, it would be something like: "You invited the
guy directly [probably for a job offer] so it would be rude not to show any
enthusiasm, something like ' _there is only YOU who can fit this position!_ '"

The くらい is to show to _which point_ the guy should show enthusiasm.  
e.g.: ― How much? ― this（くらい） much.

The なんだって is just part of the citation the person uses to express what has to
be said: "お前じゃなきゃダメなんだ" and because it is a citation, you need the って.




You got the translation wrong, it would be something like: "You invited the
guy directly [probably for a job offer] so it would be rude not to show any
enthusiasm, something like ' _there is only YOU who can fit this position!_ '"

The くらい is to show to _which point_ the guy should show enthusiasm.  
e.g.: ― How much? ― this（くらい） much.

The なんだって is just part of the citation the person uses to express what has to
be said: "お前じゃなきゃダメなんだ" and because it is a citation, you need the って.

