Just came up with another perverted idea. We could use the Multiair Fiat technology
upgrading the intake valve operation over the original head. The exhaust one remains the same.
The pushrod activates the hydraulic piston directly, with no rocker, mounted over the head (maybe an old school clearance adjustment will be needed). There will be the Multiair intake valve as big as possible, fitted with its master cylinder. And finally the electromagnetic solenoid valve. Sure it will need the computer, (mono)injection system, all the senders, etc. The camshaft duration and lift has to be similar to the original Multiair one, probably a sports camshaft would make it better.
I guess that with modern lightweight pistons and rods the above setup could reach 40hp with ease.
Just thinking out loud
Cheers