a 6X10 should technically work...BUT, a legend car is probably 10 feet without the bumpers, and 5 feet wide. so assuming you have enough length, how ya gonna get the car in there? Cant drive it because that would leave you 6 inches on either side to open the door to try to squeeeeeeeze out. If you winch it in, the winch will take up 6-8 inches of the length, so now it wont fit length wise. Also, where are you going to carry your extra tires, tools, etc.? When you add the price of a good winch, you can probably buy a 7X14 for the same price, which is the smallest I'd go...coming from a guy using a 1960's vintage open midget trailer!
My 2 Cents