Not fully solve your problem, but if You want to change the keyboard layout to english, then type at the BASIC prompt:
:UK

Hi, i have the german keyboard and would love the english one - would i be right in thinking all i need is the actual key tops and on the entire keyboard? in fact i probably on need the 10 or 15 keys that are german swapped for english.

The top of the keyboard, which is contains the keys, easy changeable.
I think firstly ask our friend, Bagpuss22, he is also live in UK. He have many Enterprises (some not working), let's ask he about keyboard swaping.
Write private message to he, because he not have to much time for reading forum.

And to go with it the english manuals would be nice.

I think the original books for sale are very-very rare.
But the most of them available for download:
http://ep.homeserver.hu/PDF/Set_Up_Guide.pdf
http://ep.homeserver.hu/PDF/EnterpriseDemonstrationManual.pdf
http://ep.homeserver.hu/PDF/Enterprise_Programming_Guide.pdf
http://ep.homeserver.hu/PDF/EXOS20_technical_information.pdf
http://ep.homeserver.hu/Dokumentacio/Konyvek/EXOS_2.1_technikal_information/index.html
http://ep.homeserver.hu/Dokumentacio/Konyvek/EXDOS/EXDOSeng.htm
http://ep.homeserver.hu/PDF/Enterprise_Application_Notes.pdf
http://ep.homeserver.hu/PDF/converting.pdf

And some Enterprise magazines:
http://ep.homeserver.hu/Dokumentacio/Ujsagok/PEM.htm

I would like to get hold of the edge connector for the mointor port please, and other connectors also.

Another ask for Bagpuss22 I have, but I think the postage cost is terrible from Hungary, firstly ask your UK friend.

I would like to get hold of the edge connector for the mointor port please, and other connectors also.

Look at this eBay auction
I think this is possible to good for the Enterprise connectors:
4 /   2 pcs.  RS Components 40 way ( Double sided = 80 way ) x 0.1" pitch , Green body White ends , no other markings , unopened packet

OK, i got my UK QWERTY layout - thanks to Bagpuss22.

just thought i would share my experiences. The main thing is; not all keys are equal, that is they are 'keyed'. when i tried to swap 'Z' and 'Y' i found that they have grooves that mean they are not inter-changeable. So i had to use the Z and Y from the keyboard sent by Bagpuss.

All working fine now, but this might be useful to someone else.