Over the years, suppliers is the Corvair world have offered aluminum pushrod tubes. I have owned sets before, but they had issues, predominantly being too thick walled at the top and impeding cold oil drain back because the thick wall was too close to the guide plates.
I wrote an article a number of years ago on how to modify the tops, but it required having a lathe, and in the end it was a lot of work for an individual builder.
Over the last several months I have designed a new set of aluminum billet tubes, had them made on very accurate CNC equipment and included details like o-ring grooves which are a few thousands larger in diameter to tighten the fit on the installed o-rings. As the picture shows, they Ave a smooth bell mouth at the top so cold oil will drain back. I include a set of Viton O-rings with each set of tubes.
To be clear, these are a ‘luxury’ item. No one has to buy these to build and fly a corvair engine. They are just an available option, a choice for builders. Guys working of a budget can always clean and paint, or powder coat stock tubes, I did it for the last 34 years.
I’m going to include these with every kit motor I sell from here forward. They look good and are a bit lighter than stock ones, but the other factor for me is it takes time for me to prep stock tubes for kit engines, and I never have enough hours in the day. These tubes, coming right out a box, saves me about 2 man hours on an engine. I offer them so builders have the same choice.