TIG welding aluminum successfully requires a LOT of practice. If you are not experienced with TIG on aluminum suggest you practice every chance you get for 6 months or a year before you try the flange to cylinder joint in your picture.

It will weld a lot easier if both pieces are same thickness of metal.

Be sure to choose a weldable grade of aluminum alloy for the parts – some grades of aluminum are very difficult to weld.

Check with your welder supplier that the TIG machine you buy is rated for the very high current and the correct waveforms/starting profile needed for aluminum welding, also be sure to use the right gas mix for aluminum.

For the cylinder to cool properly you will need a perfect fit between the CI liner and the Al cylinder. Any gaps and heat will not transfer properly. I would not recommend the liner approach for a very small air cooled engine. I have seen some successful ones but the liner in those engines had the aluminum cast directly around the CI liner, with the liner preheated to just below the temp of the melted aluminum.

If you made your cylinder from a piece of Durabar continuous cast iron in one piece you will have a durable cylinder that is one piece with no welding needed, wears very slowly, and transfers heat perfectly, as well as machining beautifully.

JD