at this point, you should probably unbolt the engines, and stick the briggs on the two seater. that is, if the the chain from the two seater will fit the clutch on the briggs. the two seater is more complete, minus a running engine. a band brake will cost 10 to 15. if the chain will fit, remove it and let soak in oil or spray down with wd40 or other penetrating lube, around $5 a can. if spraying the chain with lube, reinstall on sprockets and turn the wheel. working the wheel back and forth may get the chain loosened enough. watch your fingers, chains bite hard. if the chain just will not loosen up, replace it. buying chain in a 10' roll is around the same price as getting the exact length from a mower shop. if the return springs are doing their jobs, you can leave them in place for saturday. finding a good proper length return spring without getting a factory one can be a pain. are all the tires on both karts the same size? if so swap one over.