driveshaft for 440/727 for 1970 dart

Yeah, don't waste time looking for a driveshaft. New, better, stronger with 3" seamless tubing can be had custom made for between 2-300, depending on what parts you supply. The slip yokes are expensive. Measure for it after the tranny is in with the suspension unloaded, so you're using all but an eighth inch of the spline and it will be as strong as you can possibly have it. You'll need it with the 440 if you have any traction.