Starting problem -'71 340 Duster

As suggested prior, ensure all your conections are "clean" and tight. If your (+) lead is covered by rubber, insure no acid has gone under it and eaten away or though the wires, this would also reduce you starting current.

How olds the battery?
As well, if still no joy and to eleminate the battery, you may want to take it in for a bench test. Batterys will brake down in time. They will show 12volts (the push) no problem, however the amps within could be gone. Basicly the cells within the battery can be shot requiring a replacement. Any recharging of this kind of problem I believe will not help this situation.