personally I would cut the upper a-arm mount tubes out of the frame, weld a cross tube in the front and back then reweld the a-arm mount tubes (or fab new ones) back in, in a location where you could put new mounting tabs in the 450's location.. think it out, should take about 2 hours to do, just remember you need to get the steering shaft back in about the same location. foreward or back can be off a little but up and down on the shaft need to be pretty close.