Hey steviep, its literally a 2 minute job to unscrew the door skin and whip out the old speaker.
Having just installed my new speakers Im not that keen on taking them out.
I'll measure the origianl ford ones that I took out for you
I do remember measuring the distance before I would have trouble with the windows and from memory it was no deeper that 75mm, ie a speaker no deeper than 75mm.

Hope this is of some help