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.
