If you screen capture the image off ebay and blow it up a bit it looks like some welding may have been involved in the process.
The fabricator appears to have grafted two inch risers onto the head (like those found on a Fenton dual) - complete with studs so that the carbs can bolt on.
I am curious about internal sealing as well - a threaded nipple is certainly a feasible approach. But I would think the the top of the head has more thickness for threading then the roof of the intake - so sealing the bottom with threads seems dicey. The old speed manuals warn about 'taking to much off the top' when porting.
As for the original intake ports - they look like they have been stuffed . . . old world engineering indeed.
