I would NOT collect these plants now. I would wait until after bloom next spring. If you collect now, you risk losing the plants to winter kill and rot.
The biggest problem with collecting big wisteria (over 3 inches up to 24 inches in diameter) is not roots. Roots are never a problem with wisteria. They're rampant growers--except in the North...They will root in almost anything in a matter of days (At least here in Va.).
The biggest problem with collecting "wild" wisteria is dieback and trunk rot.
Wisteria can be pretty much collected anytime (outside of winter and later summer--which leaves it with no time to reroot and prepare for winter--if you don't have a storage area that's frost free), with little or even no roots. With larger specimens (over 3 inches or so), trunk dieback is a big issue. If you dig a big or huge trunk (don't be afraid of HUGE trunks by the way--24" trunks aren't unheard of--as they can be dug easily too) with no roots, you WILL get a lot of dead trunk down the road and possibly a dead wisteria in a couple of years. Since wisteria wood is extremely soft and prone to rot, big trunks have a tendency to "dissolve" into ghosts of their former selves even if they re-root. Same for big pruning wounds, rot sets in very quickly when branching is removed.
The best way to avoid this if you find a notable specimen with a great trunk is GRADUAL removal. You can sever many of the larger roots with a handsaw --skip the shovel--find the primaries by digging around the base of the trunk with your hands. You will most likely find dozens of roots. Sever about HALF of the really big ones and all of the small ones, backfill with eight or nine inches of forest soil. Come back next year to remove the plant--
Do not use a truck or other drastic measures to collect it, if its trunk is a good one--you will destroy it---See above--wisteria wood is extremely weak. Use a hand trowel, hand pruner, handsaw and iron prybar for the removal work. Shovels are OK, but aren't really necessary either. You will make more progress by simply getting on the ground and working with the trowel to unearth roots, severing them with the hand pruner or saw.