I would strongly recommend getting a few good books on the subject of steam and of wooden boat building. This is a good way to start as it puts you in touch with most of the problems that you will encounter as well as the solutions to those problems. Also with steam books, it shows what types of Marine Engines are normally used in models, and also the building of them. I most certainly recommend the following without a shadow of a doubt, as I have read them, and reread them. Knowledge before the event is always a good thing, as no one can know everything that is required to be know, and there are also so many different approaches to the same solution. Here are the books in no particular order:
Building Classic Samall Craft Complete Plans and Instructions for 47 Boats. by John Gardner.
This is a first class book and is regarded as the definitive work on the subject.
Model Maritime Steam by Stan Bray.
This is a good informative book and one I have found very interesting as it covers many different type of steam marine engines and their construction. This includes triple expansion engines. Boiler construction is dealt with as are fittings and firing methods along with many other interesting and relevant bits and pieces.
Model Stationary and Marine Steam Engines by K.N. Harris
This is a first class work on the subject and is as relative today as the day it was written.
Planking Techniques for Model Ship Builders By Donald Dressel.
This deals with the subject in a very informative way and makes for interesting reading, or at least I have found it so.
You local Public Library ought to have some books on the different subjects that you will encounter in the planning, construction and running of your model of Shamrock. Also bear in mind that most books can be acquired on your behalf by the local library via the Inter Library Loan System.
Please note that they are many other books on the subject, that no doubt are equally as informative, its just that I have these in my library, and can only comment on the ones I have read and studied.
If you join a local engineering society, then they may well have a large selection of books and magazines on the subjects of wooden boat construction and steam engines and their boilers etc. This should be right up your street as most, not all build steam locomotives, and as Shamrock has a locomotive boiler, then it may be only a matter of time before you lay your hands on a drawing of the locomotive. Also try the National Railway Museum at York, they might be able to help. A letter requesting to see if they have drawing of the loco in question, accompanied with an SSAE, should bring some results, if only as an elimination process. Also a similar request to the editor of the Model Engineer should bring a response from some of the readers. One thing that modeller are very good at, that is reaching out and helping their fellow modeller when help is sought.
Also visits to preserved railways can bring good results as some still sell second hand books and magazines.
Often a book or two of relevance can be found in the corner of Charity Shops, of which most high streets seem to have an abundance of these day. The seeking out of information is all part of the project,and it is very important tool of the educational variety.
Happy Modelling