OK I I have to get my driveshaft shortened for the 727 that is going in... I have been reading up on past posts and I'm looking at getting it shortened 4 inches... is this correct?

Best to measure it. If the trans is installed jack up the rear and put jack stands under the diff so the suspension is loaded. Measure from the end of the output shaft to the flat surface on the rear yoke and give that measurement to the driveline shop.

Better yet if you have a place in mind to shorten and balance it call them and ask what they want you to measure.

I just had my shaft done a few weeks ago and what I described is what they asked for.

You will also need a 727 yoke. More than likely it will take the same u/joint.

best to measure it to be sure,cost is less to shorten it than to lengthen

most shops want the it measured from center of cap to center of cap

I slide the yoke into the tranz till it bottoms out,then measure from center of cap to center of cap,then subtract 1"

thats with a flat seal with no dust boot on it

the 727 takes a bigger yoke with a diff spline count,same as the 883/883 od tranz

jack stands under axle so the springs are loaded. 727 yoke all the way in trans. measure C to C. subtract 3/4" (aftermarket common flat type seal as opposed to OE balloon seal). give them that dimention. As said check that the 727 yoke is the small u joint one (2&1/8" between the ears as opposed to 2&5/8") same as the 2&1/8 ujoint on the 904 shaft & if not get the combo joint

RapidRobert is "Right"