I have a twin 3ft tube Fluorescent street light from the 60s It has the super heavy ballast transformer, will that work ok with modern tubes? Someone was saying it’s a fire hazard.

As long as it's the same wattage that the ballast specifies, I don't see a problem.

If the wiring or connection points are failing, then you might have a hazard.

If you run it for several hours and then measure the temperature of the components, you'll get to see if it heats up too much or not.

Any equipment can fail. It must be built in a way that safely contains the fault - A streetlight does this if it is run with all required covers in place