In-op heater ... help!

[Kiwi]

I have a 1971 C-10 (350 V-8, auto, RWD, long wheelbase) that originally had factory A/C ... but at some point the compressor was removed by a previous owner.

When I slide the dash controls between hot and cold, I can hear things moving and I can feel a temperature difference. However, when I move the fan switch nothing happens. I recently replaced the main fan switch on the dash ... but the fan still does not come on. At this point I guess it could be one of four things ...

1. Blower motor needs to be replaced ... http://www.lmctruck.com/icatalog/cb/full.aspx?Page=119
2. Blower motor resitor needs to be replaced ... http://www.classicindustries.com/search?q=G9825
3. Blower motor relay needs to be replaced ... http://www.classicindustries.com/search?q=AP5760
4. A bad ground and/or power wire
5. Or ???

Does anyone have a suggestion on how to make the blower work? Is this a common problem that is easily fixed?