68 valiant signet

mpgmike said
If you have hardened seats for unleaded fuel, you should have no issues. I'm guessing you're looking at an Impco carb style system, where the intake flows both air and fuel. There are newer systems out with individual injectors at the port for better drivability; though it requires more expensive hardware and electronics (with tuning often), and probably intake manifold modifications.

Issues of running propane usually happen on Diesel engines. They still spray a little diesel fuel into the cylinder to act as a "liquid spark plug". Older systems would try running as much as 70% propane. This caused catastrophic failures, as the vaporizing diesel fuel acted as an internal coolant.

I'm not aware of any issues running propane on gasoline engines. It has excellent octane characteristics, making it good for high compression & boosted applications. Of course, make sure you have a filling station nearby.

yes the impco 425 type that bolt directly to a holley carb's base plate. re a filling station, my plan is to have a smaller 'donut' tank in the spare wheel well as a spare with the filler as per normal to use filling stations but the 'main' tank will be the orange propane tanks as used on home cooking/heating setups. i can get these from a tool hire shop down the road from me at roughly 1/3 the cost of filling stations and 1/6 the cost of petrol. it'll make the car very cheap to run with the option to switch to the refillable tank if on a long journey. i ran a '78 chevy blazer as my daily that had the really old ring over the carb lpg conversion for almost 2 years, i never used petrol ever and £ for £ (compared to petrol) it achieved 27mpg and that was buying lpg from the filling stations.
neil.