Go to the Motor Boy's web site. I am designing and building my first engine too and their website has told me just about every thing I need to know.
http://modelenginenews.org/index.html
There is a source page on their website that has just about every good website out there.
There is also a website called animated engines that may or may not be of help.
http://www.animatedengines.com/
Do you have all the tools?
Also try liney machine, they offer a variety or steam engine kits and such.
sites.google.com/site/lineymachine/
Hope this helps and good luck.