Originally posted by techinspector1
The 350 head will bolt to the 305 block, but you'd be going in the wrong direction. Propane is a high octane fuel and will support a much higher compression ratio than gasoline will. Depending on what the 350 head came off of, the chambers could be anywhere from 64 to 76 cc's. The 305 heads were 58 to 60 cc's, so you'd be lowering c.r. when you should be raising it. Although remote, there is a possibility of mechanical interference between the intake valve and the edge of the bore. Even if there is no mechanical interference, there will most certainly be a mixture flow problem as the mixture hits the ledge formed by the block deck because of the smaller bore as the mixture finds its way past the valve. I can see this combination working the other way, a 350 block with 305 heads to raise c.r. and take advantage of propane's higher octane rating.

Here's an interesting link to the new Ford head that Jon Kaase developed. It substantiates the importance of keeping the intake valve away from the cylinder wall.
http://www.jonkaaseracingengines.com...d_s_new_s.html
thanks techinspector1 I realy need to learn something today thats some good info