I ran a dual fuel system and am now converting to 100% LPG (butane/propane mixture) since it is readily available here. It is cheap too and indeed has a high octane number, so high compression is a +.
(10.5:1 for me)
It is very common overhere and I would say about 1/2 the US classic cars here run it.
www.pro-touring.nl
pages 16 & 34
www.propaneguy.com also has some info (and stuff for sale)
http://fuelsforum.rasoenterprises.com/ also a good link.....
Martin