You can build a regulated powersupply on the basis of a lm 723 with a lot of heatsink & transistors .http://agurk.dk/bjarke/Projects/PowerSupplyFET/13.8V%2040A%20Power%20Supply%20Schematic%20Prints.pdf
A schematic like this is easy adjustable to your needs .
However to limit dissapation in your transistors you could consider to add a sort of ac-ac chopper .
The idea is basicly to place mosfets between the diode bridge and the main buffer elko
(seperate the mosfets from the elko with a big sckotcky diode)
With pwm signals to the mosfets you can create a pre-regulation that can save a lot of heat
Other option is ofcourse switch mode supply's .
The following link is to a polish elektroniks magazine .
Its a schematic for a welding inverter capable of delivering 1,5 to 2 Kilowatthttp://www.ep.com.pl/pobierz.php?id=12162
For as far as i know there is no english translation of it (sorry for that)
It is possible to adjust it to your needs .
But you will have to calculate the transformer for it .
A etd59 should easily do .
But thats no project for beginners .
Good luck .