That could work depending on its configurations...if it is the typical 54 in by 36 in by 44 high. If it is the wire type, you might consider putting a cardboard liner down for better protection and comfort.
I would be a little hesitant to cram 8 bodies into 54 inches unless they are typically calm birds that are already integrated...which may not hold true in transit.
From my experience, you don't want a lot of room to move, as you don't want them able to fly (which can cause injury), but some as you don't want a dog pile. Birds can get injured or start pecking each other in dog piles. I had one breeder transport 2 Delaware hens to me in a small cardboard box with cover. When we opened it up, the one bird had dog piled on the other and pecked the other badly.
I usually transport about 4 to 5 birds in a medium dog crate for short distances (less than an hour). Longer travel may cause more stress, so you may want room to eat stuff for electrolytes (watermelon idea is also excellent...as well as apple slices).
Usually my birds simply go into a catatonic daze with the hum of the car only squawking and shuffling on sharper stops, so be prepared to move gently on turns and stopping. It's best to get started, check on everything, then go the distance unless you've got a really warm day and need to offer water.
One idea, if you have the typical large dog wire crate, you could create 2 compartment levels (upper and lower births with 4 birds each...possibly with locked dowels and thin plywood) to prevent flying as most large dog crates are about 44 inches high...room enough for flight when startled.
My thoughts. Good luck with your trip.
LofMc
