Need lot of driveshaft & 8.75" rear end help

that is the correct way to measure it. remember to back the trans yoke out of the tailshaft about an inch or so before you measure. this will give you the slack needed to get the shaft out of the pinion yoke.
i used a driveshaft out of a 70 coronet in my 64 dart, worked at stock length for a 904-to-7.25" combo but had to be cut down for the 8.75" rear, no biggie.
-tim