Mike,
Compressors and vacuum pumps are pretty much one and the same. Both use reed valves in the head to control the flow of air.
In a vacuum pump, the intake valve is located at the pipe to the reservoir, and the air exits through a muffler.
In a compressor, the intake valve is located at the filter, and the air exits through the pipe to the reservoir.
So, in some cases, you can remove the heads and swap the valves around. In other cases you can remove the filters, then remove the fittings that contain the valves, and switch them around. This is the most likely case with your unit, as near as I can tell.
I am glad that your photos finally appeared. When I was in high school, I worked part time for a neighboring farmer, and he had an air compressor that looked exactly like your vacuum pump, same color and everything!
One thing that might be a big problem is the tank. In most cases vacuum tanks would be engineered a bit differently than pressure tanks. It would be a good idea to examine the tank carefully for any indication of how much pressure the tank may be certified for. Whatever you do, please don't use the existing tank for air pressure unless it is certified for such use. None of us want to see a future post from you or a family member indicating that you were either killed or maimed when the tank blew up!
You will also need to add a pressure relief valve, of a proper setting for the pressure tank you use (this is a MUST DO!). You will probably want to add a pressure control switch also, so that once the pressure builds to an adequate set point, the compressor will shut off.
If you have further questions, feel free to post 'em here!