Yes it raises many questions! I guess it may have a roller crank, and most probable the guy used the standard bottom end and modified the piston.
Bet if you done the same thing to a newer bike you'd have no chance of getting it through emission laws - Why? Low compression - lots of emissions.
I know when I raced solo bikes we raised the compression up to around 16:1, high enough to probably ignite diesel fuel, but would guess you'd get the white/blue smoke some low compression direct injected diesels were notorious for, there still around, but being fazed out.
All the same, looking at the pics, it makes you think playing with a petrol engine could work, the Harley engine project was a good article Stuart put up on another thread.
Cheers
Andrew
Chaps, they said it couldn't be done but back in 1978 Enrico Agostini's Uncle adapted an old fiat 500 and fiat 850 coupè turbo to run on diesel as well as this 1956 Perugina 175. Many thanks to Enrico for the details and Ron who who told me about the bike. Good work guys 
