Tig welder to purchase.

[RCP57]

I don't know if you would need 300amps but you have to think about duty cycle. I think my 225 at full power has 20% duty cycle or less. It won't build heat quickly enough to weld that thickness properly. To actually get penetration on 3/4" you need an industrial welder. Just bolt those parts together or you will be spending 6k on a welder...