P-39 would be natural candidate for setup like this. What about using a carbon fiber pushrod tube? Light, strong, if it can be balanced and made to run true would be perfect. You let back end be supported by engine, support front end with thrust bearing in firewall. Would have to mount fuel tank either right in front of or behind engine, behind would be better as plane would get nose heavy as it empties. Or if plane was big enough fuel tanks in wings...... but that's getting pretty complicated.

andy