Should be a standard gm cable.. Summit has a few different lengths. You can put a wide radius loop in it if you need to. Not sure where the connection is on the 700 but I used a 55” universal for my 200.
If you are looking at the end of your stock Roto cable don’t. It’s not standard. The speedo has a stock fitting and the 700 should have a stock fitting like the speedo. It should be a regular old gm cable unless you have some one-off trans speedo housing on the 700. Maybe I’m wrong here but I don’t think so.
Are you putting in a control for the lock up converter.? I used the B&M unit and put the VSS with the short adapter cable up under the dash above the steering column brace attached to the speedo itself rather than down at the trans.