Your bug report is difficult to understand.

>
> In emacs -Q just need something to get the Alt key bound
> e.g.
> (setq  mac-command-modifier 'alt)
>
> The when you Type A-c you get ¢ and you cannot bind it yourself.
>

If you do this, A-c should display "A-c is undefined", which is indeed the 
case, it's not bound to any command (in emacs -Q).

>
> On a mac I want the key by space to be Alt as that is what is printed on 
> my PC keyboard. I suspect this is true with PCs
>

If you want the key on the left of the space bar to be the Meta key in 
Emacs (which is what the Alt key usually does), you should do: (setq 
mac-command-modifier 'meta).

>
> The issue is that (require 'iso-transl) is called before the user can 
> alter its behaviour and that iso-transl.el then binds to various A-c and 
> other keys.
>

The use of the Alt modifier is indeed hardcoded in iso-transl.  If you 
want to use it, you can chose another modifier key on your keyboard, for 
example: (setq mac-right-command-modifier 'alt).  In that case the key on 
the left of your space bar will be Meta, and the key on the right of your 
space bar will be Alt.