Question on fitting modern trans in 71 Demon

the 518 fits in the dart with out cutting the floor the chevy will cost more just because you have to get adaptor. yes you have to change the trans mount but, i think you will have to do that with the GM200. and the drive shaft will have to be altered. i think you can go to a you pull junk yard pull the 518 trans . the rest should be under 300.00, pressure switches and drive shaft.