The man I bought my 7x17 camera from did not use a Jobo. It has been a few years but if I remember correctly he said he got marks bleeding through from the ribs that run around the 3063 cylinder. I have never tried my 7x17 film in a 3063 because of that.
Instead I use 2560 and 2830 tanks connected. Two sheets of film fit into the lengthwise ribs with enough tension to keep them in place. There is only one circular rib in the middle and it does not leave a mark. Perhaps there is another tank combination that would accommodate 8x20 with ribs at 8 inches. The combined tanks are 21 inches deep.
I use Bostick & Sullivan's rollo pyro developer on HP5+, FP4+ and T Max 400. There is a 5 minute prewash then the developer, speed setting "4", 68 degrees F, and dump at 6 minutes. It takes about 20 seconds for the developer to pour out and another 20 seconds for the first water stop to get in, so development is really longer than 6 minutes. I have been adjusting all this for about four years. Good luck. Hope that helps.