904 slip-yoke

No, don't need one. I'm looking at replacing the 7 1/4 with an 8 1/4 and figuring out what driveshaft will be needed. From research, I know that he can measure the existing driveshaft and subtract 1.25" from that to get the length of what is needed.
He's gonna have to drive 200 miles to my house for me to do the swap. Just trying to get everything lined up beforehand. Thanks