My 1974 mobile home has old coleman furnace that worked fine the passed 3 years. Now, I turn it on and it runs for as long as it is turned on without blowing hot or cold air. Do I assume it's the blower or could it be a combination of problems.

Well, it could be the blower motor, but it could also be the blower control or relay. The part that is scary, is that the flame never shuts down. When the blower doesn't kick on after a minute or two, the high limit should trip and shut the gas valve off. If this is the case, and the flame never shuts off, you have a very serious safety issue, and need to have a service tech out asap. Shut the unit off until one can get there, or you may burn that sucker down. Really sounds like you may have a faulty fan/limit control, or as you already guessed, a combination of problems.