jeep seat mounting question

i am having a problem mounting the seats in my 77 cj5. it looks as though someone welded brackets onto seats that don't belong, then welded them to the floor of the jeep. what is the best way to break welds? what kinds of hardware am i going to need to install my new seats?

 

Best thing I've found for cutting welds and/or sheet metal is a four inch angle grinder fitted with a 4" or 4 1/2" metal cutting blade (can get them at any hardware). Just be careful with it. Use gloves and eye protection. The brackets you go back with depends upon what you want.
Good luck.