Need some advice.  I have a 4100 carburetor I'm rebuilding for my 57 312 I've built.  My problem is the choke tube that goes through the base of the intake manifold is rusted out.  Are these choke tubes available anywhere?  I've checked into installing an electric conversion kit choke but I read where they do not work good because the choke opens up in about a minute which is to fast.  Any suggestions other than installing a manual choke?  

buddy