ゴリラが頭を掻いてる姿がダドリーそっくりだ。あれで金髪だったらな.....。(ellipsis as written)
The gorilla scratching its head looked just like Dudley. ????
I don't know what あれで金髪だったらな means or what the grammar is. Guesses are "If only it were blond...", "Except it wasn't blond..." etc.
Obviously 金髪だったら is "if it were blond", but I have no idea what あれで is doing or what な is doing. The dictionary says あれで means "despite appearances" but that makes no sense to me.
あれで is equivalent to あの様でいて, whose literal translation is "(That thing) exists in that way (and/but)".
Thus it can be used as
あの様でいて、さらに金髪だったらもっと彼に似ているのになぁ
which can be shortened to:
あれで金髪だったらもっと似ているのになぁ
and then further to:
あれで金髪だったらなぁ
What exactly is shortened needs to be guessed, so I can't be 100% sure what is implied, but one interpretation here is that the way the gorilla exists (appears) already resembles Dudley, and if it had blond hair on top of that it would resemble him even more. Another valid example interpretation would be あの様でいて、さらに金髪だったらもっと好きになるのに (which, however, seems less likely given the context!).
The "despite appearance" usage can be explained as follows.
Something like this:
あの様に自信ありげでいて、実は小心者なのだ
can be shortened to:
あの様でいて、実は小心者なのだ
and this further to:
あれで小心者なのだ
which implies, despite this person looking confident, they are actually anxious (again, what exactly is implied by the last sentence needs to be guessed).
