Hi Deiter

It is most likely that you have an 1800cc engine from an MGB but it is possible that you have something else. The MGB engine is what we call a "B" series engine and is similar to the one in many British Leyland vehicles of the time.
If you have one of these, I agree with Mike, it is best to purchase a Haynes Workshop Manual (no. 111). If you have difficulty you can get it direct from their web site at www.haynes.co.uk.
Alternatively you could try the MG Owners Club www.mgownersclub.co.uk who have a variety of books for sale as well.
You may also be interested in my web site about the building of a TF - www.ngkitcar.co.uk.
Hope that helps!