i fit mine in the hatch to get it to the bodyshop, had to take it out of the box to get it fit with the new bumper, fender, bumper reinforcement, and all the other parts that were damaged.
OK I just took some measurements because I was curious. A hood is 49" wide. The widest part between the inner quarter panel plastic on a 87-89 Hatch is about 50" (the section above the speaker enclosures). On a 90-93 however the widest part is about 44" due to the 3 point rear seat belt mounts. So the answer is, it depends on what interior you have, 87-89 (yes) or 90-93 (no). You might be able to wedge a hood in a 90-93, but it won't fit in fully with the hatch closed like in a 87-89.
Ok, so i had to comment because i just went through this with a hatch. I found a non rusted hatch for mine recently and had to call a friend with a truck to get the hatch home. Those things are bigger than they look for sure. I tried fitting it in a new hatch back car that i thought had lots of height, so no go, then tried a the back of a Durango....no go either......so, the truck got used....
LOL! I've also brought home a nice rust free hatch, in the back of my hatchback LX. I stumbled on it at our local Pick a Part during lunch. Well, knowing it would not last long at all, I called my boss and asked for the afternoon off. So I pulled it (in my work clothes, none the less, business casual!) and wedged it in my hatch with the end sticking out about 10" past the tail lights. I tied my hatch down, but I hit a bump on the way home and the #$%^& latch put a couple of dents in the new hatch! $%^&*#$%^!!! Oh well, at least it is not rusting out like my original one was, plus it is a GT hatch, perfect for the GT spoiler I already had. You can haul a LOT in the hatchback Mustangs if you need to, believe me I've done it. A dishwasher one time, TWO swivel rockers another (both with the hatch closed!) 4x8 Sheets of plywood (before the 90 interior swap) and many other things.
I have been surprised at what I've been able to squeeze into the back of a hatch Mustang, it's like a spare pickup.