Hi, I have a 69 charger with a 383/727 8 3/4 set up. Its missing the driveshaft.The book is calling for 52.07 length and 3" diameter I believe. I found someone with a shaft that is measuring 51 1/4 from the center of both u-joint holes.He thinks its 3 1/4 diameter.Do you guys think this will work or no? Will the yoke take up the 3/4 inch or so? Thanks for any help!

Won't work. It will cause the yoke to be too far out of the housing which leads to wobble and will wipe out the rear trans bushing and housing. For a correct fit the yoke will only be 3/4 to 1' away from bottomed out.

Thanks for the reply. Thats what I was wondering about.Hard to believe 3/4 of an inch would make such a difference.It does make sense due to what force goes through it though.Thanks for the input again,I'll have to keep looking.

shove yoke all the way in till bottomed out

measure from center of u-joint cap to center of u-joint cap

subtract 1"

size round can be bigger or smaller around...just not too skinny

get one from a wagon/c-body or something and have it cut down and balanced

thats they way I build them swaping drive lines around

You can often fit a longer than factory length driveshaft in place. As long as it doesn't bottom out. 3/4" - 1" is all the yoke clearance needed.
Shorten than factory length is a definate recipe for vibration or worse tailshaft breakage.