Ok... so I went to Radio Shack to get the parts...
They don't carry the 7806 or 7808 regulator.
They don't carry the 2N5881 transistor either.
Resistors, diodes, caps no problem.
Soooooo... I am trying another route...
Using a LM317T variable regulator with a potentiometer. the result should give me an ADJUSTABLE output range of 1.2V to 13.8V. Used in conjunction with a 2N3055 transistor, I should get up to 15 Amps of current capacity.
I will try to get it done today and will post my results. Once it is tested, I will post a schematic.
If it works, I may be interested in marketing the whole assembly. It seems like there is quite a demand for a 12V primary - 6V secondary power supply, and nothing commercially available.