7 1/4 to 8 1/4 swap

I’m doing the same deal, is the 1 inch pretty standard for that?
Yes, but nothing beats measuring just to make sure. When I did mine, I had a spare driveshaft from a car with an 8.75- it fit perfectly, so I didn't have to have one cut. It was a little over 1" shorter (tape measure, so take it with a grain of salt- could be 1, 1 1/8, 1 1/2, etc.).
This thread seems to agree on 1 1/4- 1 5/8...
7.25" to 8.25" driveshaft? | For A Bodies Only Mopar Forum