There is really only one essential tool for dismantling an ETZ251 engine and that is a proper workshop heavy duty clutch puller. You can buy smaller cheaper ones for very little money but they may not work and could well damage something. The clutch can be very tight. The other really useful tool which can be fabricated from a strong piece of angle iron is a bridge to separate the crankcases. If you look on ebay you will see examples of both tools. Apart from that its common sense but do make sure you heat things up when dismantling and reassembling. A Haynes manual or better still a workshop manual from the Regalia Shop are strongly recommended.
Afraid I don’t know where you can beg/borrow one, you really need to make contact with an MZ owner in your local area. Suggest if you have not already done so that you contact your local section rep Dave Gillespie who can probably put you in contact with someone close who can help. Dave’s details are in MZ Rider.
Hope that helps