If this is a DIY project: 6 inch pipe would not be sufficient for the 30 inch side of the paper. You would need ~6.5 inch diameter tubing which would be hard to find. So you could get 8 inch tubing which will accommodate the 40 inch side and then use a 30+ inch length of it. Not all PVC pipe is light proof from what I understand. If you used 36 inch wallpaper troughs, you could leave one end of the tube open and spin the tubes in the trough under safelight.
I think the largest Jobo tank is the 3063 for 20x24 inch.