It's not enough for Madhosue Mode to have more monsters, less ammo, and fewer saves- they also gotta mixup where all your stuff is kept. Here's the key to where everything is now, and to which things are just as you left them.
Unchanged:
All video locations and flashbacks remain the same, though the enemies in the final flashback are tougher.
The locations of Journal Entries & Mr. Everywhere Bobbleheads are unchanged.
All Treasure Photos are found in the same place, and yield the same treasures as before
All special key doors (Scorpion, Crow & Snake) are in the same places, leading to the same rooms. The Crow and Snake Keys are in the same places as before (The Scorpion Key is now in a coin cage in the Main Hall).
The access cards are in the same places, and obtained the same way as before.
Weapon Locations
The knife you still get from the deputy, but it's a mere toothpick next to the Circular Saw
The G-17 is still in the garage, but it's now lying where the deputy fell, rather than in the backseat of the car.
The M-19 is now in the Greenhouse entry, rather than in Zoe's Trailer
The Grenade Launcher is now in Zoe's Trailer, rather than in the Crow Room of the Main House.
The two shotguns are in the same places, but the Model Shotgun in now is the Dissection Room- you can grab it when you make for the third dogshead here.
The flamethrower components are in the same places.
The Survival Knife is now stuck in a ping-pong table in the Recreation Room
The MPM Handgun is now in Sickbay
The Machine Gun and key are in the same places.