Here is the fuel tank on my version of my just completed Rupnow vertical
The tank is all stainless steel 28mm dia tube 70mm long with a 2 mm wall
The ends are a light press fit with a smear of green loctite.
if you want to build a i/c engine then the Webster is a good place to start. There are several build threads on the making of this engine you can find the plans here Free Plan: Webster Engine Work's 4-Cycle Gas Engine | MachinistBlog.com