Neurosurgeon
I wouldn't want a steel cylinder pressurised to 250-odd Bars with a combustible gas anywhere near my nether regions. I suppose you could find people who love to live life on the edge...
The "dry" gas would grind the valve seats into submission, that said, aren't there hardened valve seat inserts available for "unleaded"-ing cars of that vintage? If one is feeling rather courageous, valve seats from another engine may be turned down to fit. Long days in the junkyard with a set of vernier calipers would be needed...
devilstone
There were a few scooter prototypes that ran on CNG, but I don't know if any made it to production.